Class S h'U i 
Book ' 

CopightN" 

CXIPffllGHT DEPOSm 



DISEASES OF GREENHOUSE CROPS 
AND THEIR CONTROL 



OTHER WORKS 
BY THE SAME AUTHOR 



The Culture and Diseases of 
the Sweet Pea - $2.50 net 

Illustrated 

Diseases of Truck Crops and 
Their Control - $5.00 net 

Illustrated 

Diseases of the Sweet Potato 

(In Preparation) 



E. P. DUTTON & COMPANY 
NEW YORK 



DISEASES 
OF GREENHOUSE CROPS 

AND THEIR CONTROL 

BY 

J. J. TAUBENHAUS, Ph.D. 

Chief of the Division of Plant Pathology and Physiology. Texas 
Agri-ultural Experiment Station, Agricultural and Mechanical College of Texas 
Author of "The Culture and Diseases of the Sweet Pea" 
"Truck Crop Diseases and their Control" 




NEW YORK 
E. P. DUTTON & COMPANY 
68 1 FIFTH AVENUE 



Copyright, 1920, 
By E. p. DUTTON & COMPANY 
All Rights Reserved 




PRINTED IN THE UNITED STATES OF AMERICA 

©G!.A570968 



THI5 BOOK IS AFFECTIONATELY 

DEDICATED TO MY WIFE 



t 



INTRODUCTION 



The art of forcing vegetables and flowers is not a 
new one; however, its economic aspect is of modem 
origin. The Thirteenth Census of the United States 
estimates that the total area of land under glass in 
1909 was 114,655,000 square feet, of which 
105,166,000 square feet were in greenhouses and 
9,490,000 feet were covered by sashes and frames. 
About 99% of the value of the plants and flowers 
in 1909 was produced in 7,444 establishments, the 
average value of each of these establishments be- 
ing $4,630.00. As is natural to expect, these estab- 
lishments were located near large cities. The lead- 
ing states in value of forced flowers and plants were 
New York with $5,110,000; Pennsylvania with 
$3,761,000; Illinois with $3,681,000; New Jersey 
with $2,839,000; Massachusetts with $2,432,000; 
Ohio with $2,357,000; California with $1,374,000; 
Indiana with $1,202,000; Michigan with $1,132,- 
000; and Connecticut with $1,042,000. States with 
less than a million are not here recorded. The total 
value of forced plants and flowers as estimated for 
1909 was $24,930,000. 

There are as yet no available figures of the area 
and the money value of the greenhouse industry. 
It is, however, reasonable to suppose that the num- 

vii 



viii 



Introduction 



ber of establishments and their money value have 
lately increased by at least fifty per cent. This, 
therefore, represents a vast sum of money and an 
important industry of the United States which can- 
not be ignored. 

Plants under greenhouse culture are far from 
being subjected to normal conditions. The expres- 
sion ''tender as a hothouse plant" well expresses 
the truth. Because of this fact greenhouse plants 
are naturally more susceptible to diseases indoors 
than similar plants grown in the open. This at once 
emphasizes the importance of studying the diseases 
of greenhouse crops with a view to furnishing the 
growers such information as may help them to re- 
duce important plant diseases and thereby increase 
their profits. We have as yet no available figures as 
to the money losses from diseases of greenhouse 
crops. A conservative estimate, however, may place 
these losses at about thirty per cent. 

The literature on diseases of greenhouse crops in 
the United States is rather fragmentary and scat- 
tered. The American Plant Pathologists have been 
too busy in devoting much time to the investigations 
of the diseases of cereals, fruit and truck crops. 
Considering that plant pathology is only a new sci- 
ence, the diseases of the greenhouse crops had of ne- 
cessity to be neglected. It is, therefore, the aim and 
purpose of the present volume to bring together 
available information on the subject and to place it 
at the disposal of the greenhouse men. The author 
realizes too well the incompleteness of this work; 



Introduction 



ix 



however, it is felt that no apologies are due and it is 
hoped that it will meet an important demand for 
information, and stimulate further research in this 
line. The book is intended as a guide to practical 
growers, teachers, students and investigators in plant 
pathology. It is taken for granted that the practical 
man who uses this volume will study it with a view 
to gathering information to serve him as a guide, as 
no definite hard rules are here laid down which could 
apply to the problems of each individual case. It 
is only by combining the information with good 
common sense that the best results are to be ob- 
tained. Constructive criticism is solicited and help- 
ful suggestions will be gratefully received. 

Acknowledgments are here due to Dr. and Mrs. 
D. de Sola Pool of New York City; Dr. 1. Adler- 
blum, Statistician of the Metropolitan Life Insur- 
ance Company, New York City; Professor R. B. 
Brackett, Professor of English of the Texas A. and 
M. College; Professor S. C. Hoyle, Editor Exten- 
sion Service Publication, Texas A. and M. College, 
for helpful criticisms and for reading the manu- 
script and proofs; to Professor F. B. Paddock, 
Entomologist, Texas A. and M. Agricultural Ex- 
periment Station, for reading the proofs; Miss 
Florence Buckman of the Plant Pathology Divi- 
sion, Texas Experiment Station for assistance in 
preparing the glossary and the index. 

Grateful acknowledgments are further due to 
Dr. C. G. Hopkins for fig. 2a, Dr. T. F. Manns for 
fig. 2b, Professor L. Green for fig. 5a, Professor L. 



X 



Introduction 



E. Melchers for figs. 8a, b, and c, Dr. Clinton for 
figs. i6b, 38a and 40b, Professor R. E. Smith for fig. 
22, Miss Nelly Brown for fig. 26, Professor A. D. 
Selby for fig. 28a, Professor Edson for fig. 35, 
Professor H. E. Stevens for figs. 37a and b, Profes- 
sor H. S. Jackson for fig. 40a, Professor L. N. Mas- 
sey for figs. 65b and 66a, Dr. A. B. Stout for fig. 
72a, Professor Moznette for figs. 78c and d, The 
King Construction Company for figs. 25 and 45, 
The John Moninger Greenhouse Company for fig. 
52, Professor F. B. Paddock for figs. 80 and 81. 

Credit is also due to the Foley Greenhouse Manu- 
facturing Company for figs. 21, 49, 57a, 58a, 60 
and 64. The remainder of the borrowed figures are 
acknowledged in their proper places. The author 
also wishes to express his indebtedness to the Texas 
Agricultural Experiment Station for the original fig- 
ures which were taken by the Station Photographer 
for the Division of Plant Pathology and Physiology. 

J. J. Taubenhaus 

College Station, Texas 
May 1, 1919 



CONTENTS 



PART I 

CHAPTER PAGE 

I. The Healthy Soil 3 

11. Sick Soils i6 

III. Treatment of Sick Soils .... 28 

PART II 

CULTURAL considerations 

TV. Light in Its Relation to Greenhouse 

Culture 53 

V. Moisture and Water Requirements 73 

VI. Breaking the Rest Period of Plants 86 

PART III 
diseases of greenhouse vegetables 

VII. Nature of Plant Diseases ... 93 

VIII. Germination Troubles 104 

IX. Beet Diseases 114 

X. Cauliflower Diseases 122 

XI. Cucumber Diseases 133 

XII. Lettuce Diseases 145 

XIII. Mushroom Diseases 159 

XIV. Parsley Diseases 166 

XV. Radish Diseases 173 

XVI. Tomato Diseases 180 



Contents 



PART IV 

DISEASES OF ORNAMENTALS 



CHAPTER PAGE 

XVII. Alternanthera Diseases .... 200 

XVIII. Aster Diseases 207 

XIX. Carnation Diseases 217 

XX. Chrysanthemum Diseases .... 235 

XXI. Cyclamen Diseases 248 

XXII. Hyacinth Diseases . . . . . . 266 

XXIII. Lilac Diseases . 275 

XXIV. Orchid Diseases ....... 290 

XXV. Primrose Diseases 315 

XXVI. Sweet Pea Diseases 334 

XXVII. Tulip Diseases . 348 

PART V 
greenhouse pests 

XXVIII. Plant Pests . 364 

XXIX. Greenhouse Thrips 369 

PART VI 
methods of control 

XXX. Methods of Control 381 



LIST OF ILLUSTRATIONS 

FIGURE FACING PAGE 

1. Effect of Fertilizers and Watering on the Yield 

of Lettuce 5 

2. Effect of a Balanced Fertilizer on Corn and 

Clover 9 

3. Conidiophore and Conidia of Pythium . . 19 

4. Nematode 25 

5. Leaf Blight Nematode 27 ' 

6. Steam Sterilization Apparatus 37 v 

7. Effect of Soil Sterilization 39 

8. Melcher's Soil Sterilizer 43 

9. Action of Different Light Rays on Coleus and 

on Lettuce 63 

10. Action of Different Light Rays on the Color of 

Plants 65 

11. Sling Psychrometer 77 

12. Effect of Subirrigation on Lettuce .... 85 

13. Effect of Etherization on Plants .... 87' 

14. Effect of Etherization on Hybiscus syriacus . 89 ' 

15. Bean Diseases 111/ 

16. Beet Diseases 115 

17. Cauliflower Disease . 123 

18. Celery Disease 131 

19. Celery Disease 133 

20. Young Healthy Greenhouse Cucumber Plants 135 

21. Cucumber Diseases . . 137 ^ 

22. Cucumber Root Knot 141 

23. Egg Plant Diseases 143 

24. Egg Plant Diseases 145 

xiii 



xiv List of Illustrations 

FIGURE FACING PAGE 

25. Type of Lettuce House 147 

26. Lettuce Diseases 149 

27. Lettuce Diseases 151*' 

28. Lettuce Diseases 153 - 

29. Typical Muskmelon House I5S 

30. Muskmelon Diseases 157'' 

31. Root Knot of Muskmelon 159 

32. Healthy Mushroom Bed i6iv 

33. Sclerotinia Rot on Pea Pods 167 ^ 

34. Pepper Diseases 169 1 

35. Rheosporangium Rot on Radish .... 175 

36. Tomato Diseases 193 

37. Tomato Diseases 194 ■ 

38. Tomato Diseases 195 

39. Effect of Fumigation on Tomatoes .... 197 

40. Anthirrhinum Diseases 203 

41. Anthirrhinum Diseases 205- 

42. Aster Diseases 209 ' 

43. Begonia Root Knot 213 

44. Calceolaria Leaf Blight 215 

45. Type of Carnation House 217 

46. Carnation Diseases 223 

47. Carnation Diseases 227 

48. Carnation Diseases 229 

49. Type of Chrysanthemum House . . . .235 

50. Chrysanthemum Diseases 237 

51. Broom Rope of Coleus 245 

52. Type of Cyclamen House 249 

53. Dracena Diseases 251 

54. Fern Yellows 255 

55. Fern Diseases 257 

56. Geranium Diseases 261 

57. Hyacinth Diseases 267 

58. Lily Diseases 277 



List of Illustrations xv 

FIGURE PACING PAGE 

59. Orchid Diseases 295 

60. Type of Palm House 307 

61. Palm Diseases . 309 

62. Pansy Diseases 311 

63. Primrose Diseases 315 

64. Rose House . 319 

65. Rose Diseases 321 

66. Rose Diseases 325 

67. Rose Diseases 329 

68. Rubber Plant and Schizanthus Diseases . .331 

69. Sweet Pea Diseases 335 

70. Sweet Pea Diseases 341 

71. Sweet Pea Diseases 347 

72. Tulip Diseases 349 

73. Violet Diseases 355 

74. Violet Diseases 357 

75. Violet Diseases 359 

76. Red Spider 365 

77. Mite Injury of Geranium and Cyclamen . . 367 

78. Snapdragon Mite Injury 369 

79. Snapdragon and Geranium Mite Injury . . 370 

80. Plant Aphids 371 

81. Bucket Spray Pump 407 

82. Violet Cuttings 409 



PART I 



CHAPTER 1 



THE HEALTHY SOIL 

An intelligent understanding of the soil is of para- 
mount importance to the success of the greenhouse. 
There are three important points that we must con- 
sider in the study of a healthy soil. They are : ( i ) 
texture, (2) fertilizers, (3) soil flora. 

Texture 

Texture deals with the character of the particles 
which make up a soil, and with their arrangement 
in relation to each other. Clay soils are generally 
made up of very minute particles. Silt is made up 
of large grains. Coarse sand or gravel is composed 
of the largest grains. A soil is said to be porous 
when air or water can circulate through it freely. 
The porosity depends on the various proportions of 
clay, silt and sand which that soil contains. Plant 
growth, and incidentally plant health, is closely in- 
terwoven with the soil structure. Compact, sticky 
clays will be far more unfavorable to greenhouse 
crops than a clay loam. 

The greenhouse man has the advantage over the 
ordinary farmer because he can modify the texture 

3 



4 Diseases of Greenhouse Crops 



of his soil so as to make it ideal for his crops. By 
combining the proper amounts of clay, silt, sand and 
humus, he may give to the plants a most congenial 
place to thrive in. To obtain such a result the gar- 
dener must exercise his best judgment. By varying 
the texture of the soil we may often influence the 
plants unfavorably. Flowering plants may be made 
to produce excessive foliage and few blossoms, while 
others may be differently affected. 

Fertilizers 

Crops require certain food elements to make 
growth possible at all, and they further require spe- 
cific substances to enable them to accomplish definite 
purposes. The carnation, for instance, requires pe- 
culiar food elements to attain maximum growth. It 
further requires special nutritive elements to enable 
it to produce flowers and to avoid going altogether to 
foliage. The four leading plant foods needed by 
greenhouse crops are nitrogen, phosphorus, potassium 
and lime. All the other plant food elements are 
present in nearly all soils. 

The effect of nitrogen is to stimulate leaf and 
stem growth, and to add green color. An overdose 
of it, however, may result in soft plant tissue, and 
thus retard fruiting. Acid phosphate stimulates root 
growth, and an overdose of it encourages an excess 
of root formation over foliage. Phosphorus also 
stimulates earliness in fruiting. The effect of potas- 
sium is to help the plant in assimilating other plant 



The Healthy Soil 



5 



food, and indirectly in the manufacture of starch. 
It also encourages the production of finer plant tis- 
sue, thus increasing the plant's resistance to disease. 

The aim of the greenhouse man is to produce early 
truck crops or cut flowers and this is directly con- 
cerned with feeding. Because the four plant food 
elements above mentioned are of extreme impor- 
tance, their application cannot be indiscriminate. 
The greenhouse man must know how much of them 
to use in combination or separately. He must know 
also which element will especially benefit the par- 
ticular crop with which he deals. In his investiga- 
tions with the fertilizer requirements of lettuce, 
Stuart * reached the following conclusions : Potash 
when used in any considerable amount either alone 
or with nitrate of soda is unfavorable for growth 
(fig. 1, D.). Acid phosphate alone, in combination 
with nitrate of soda, or in combination with muriate 
of potash, stimulates growth (fig. i. A, B, C). For 
lettuce the use of chemical fertilizers proved slightly 
superior to stable manure, while nitrate of soda was 
found to be superior to dried blood. Wheeler and 
Adams,f in their work with radishes, found that an 
application of partially composted horse manure at 
the rate of 75 tons per acre gave better results than 
any other combination of fertilizers used. Work- 
ing with carnations, Darner + and his associates 

* Stuart W., Indiana Agr. Expt. Sta. Bui. 84, Vol. 10: 11 5-142, 1900. 

t Wheeler, H. J., and Adams, G. E., Rhode Island Agr. Expt. 
Sta. Bui. 128: 183-194, 1908. 

t Darner, H. B., et al., Illinois Agr. Expt. Sta. Bui. 176: 365- 
386, 1914. 



6 Diseases of Greenhouse Crops 



found that the use of nitrogen and acid phosphate 
caused an increase in the quantity and quality of the 
blossoms, but that the excessive use of potassium 
sulphate and dried blood would act injuriously on 
the plants. In his work on roses, Muncie * conclud- 
ed that nitrogen in the form of farm manure, liquid 
manure or blood is very beneficial. The same seems 
also to be true for acid phosphate when used at the 
rate of 4 to 8 tons per acre. Lime should be added 
only when necessary to sweeten the soil. In this case, 
finely ground limestone may be used as a top dress- 
ing at the rate of 10 pounds per 100 square feet of 
bench space. 

From the above discussion, it is evident that the 
proper handling of fertilizers underlies the success 
or failure of greenhouse crops. The cattleman, the 
poultryman, and others who deal with live stock 
now fully appreciate the importance of a properly 
balanced ration. Plants are similarly living organ- 
isms and consequently they too derive most benefit 
from a balanced ration (fig. 1, A.). 

Aside from a consideration of the relation of the 
fertilizer to plant growth, its relationship to the 
soil must not be overlooked. Certain fertilizers, 
such as nitrate of soda, yield a residue of sodium, 
the accumulation of which sweetens the soil, and in 
the long run makes it alkaline. In clay soils serious 
physical effects may be the consequence. On the 
other hand, muriate and sulphate of potash, and 
sulphate of ammonia leave an acid residuum, the 

•Muncie, F. W., Illinois Agr. Expt. Sta. Bui. 196: 5x1-564, 1917. 



The Healthy Soil 7 



accumulation of which may render the soil sour. It 
therefore becomes imperative to so use or to so mix 
these fertilizers that their residues will combine and 
thus neutralize each other. One reason perhaps why 
greenhouse men favor the use of manure is that they 
have experienced the bad effects of the residue of 
improperly mixed fertilizers. 

Soil Flora 

By a soil flora is meant the bacteria or fungi, 
whether beneficial or harmful, which thrive in that 
soil. Science has proved definitely that a soil can 
no longer be regarded as a conglomeration of dead, 
inert particles of rock. The soil teems with life 
which to a large extent determines its fertility. The 
more numerous the beneficial bacteria and fungi it 
contains, the more fertile it will be. On the other 
hand if the beneficial micro-organisms are absent, or 
perform their work imperfectly, or if the soil is 
overridden by harmful parasitic bacteria or fungi, 
we speak of it as a sterile or sick soil. In the green- 
house, the soil flora is often entirely different from 
what it is outdoors. This is due to the fact that the 
soil is artificially made up of a mixture of various 
ingredients with the object of making it ideal for 
plant growth. It is imperative that the greenhouse 
manager possess some knowledge of bacteria and 
fungi, and that he understand the functions and the 
requirements of the soil micro-organisms, if he wishes 



8 Diseases of Greenhouse Crops 



to secure proper control of his soil and to make it 
ideal for plant growth. 

A. Bacteria. Bacteria are minute microscopical 
plants that consist of a single cell. They are com- 
posed of a cell wall of protoplasm and average about 
1/25000 of an inch in length. These simple organ- 
isms multiply by fission, that is, the original mother 
cell divides in two equal parts, which may separate 
or remain united, giving the appearance of a thread. 
It has been estimated that a single bacterium divides 
about every twenty minutes. Granting that this 
rate of division is uninterrupted for twenty-four 
hours, the descendants of a single one within a day 
would be in round numbers 1,800,999 trillions. 
These when placed end to end would make a string 
two trillion miles long, or a thread long enough to 
go around the earth at the equator 70,000,000 times. 
However, multiplication at such a rate cannot occur 
because food conditions are restricted. The three 
main types of bacteria are : 1 . the cocci, 2. the ba- 
cilli or rods, 3. the spirilla or spirals (fig. 2, c). 
The greater number of the soil bacteria are benefi- 
cial, the most common being the saprophytes, or 
those which help to decay the dead organic matter 
from either animal or plant. The parasites on the 
other hand are those which produce disease. 

B. Fungi. Fungi are low forms of microscopic 
plants, of a slightly higher type than bacteria. Fungi 
arc made up of colorless feeding threads technically 
known as hyphse or mycelium. The spores which 
correspond to the seed of the higher plants are borne 




Fig. 2. 

a. Effect of a balanced fertilizer on corn and clover, b, various organisms 
isolated from a soil particle, c. types of bacteria, Coccus, Bacillus and Spirilla 
(after P. E. Brown); d. pycnidium (after C. L. Shear), e. conidiophores of 
Penicillium. 



The Healthy Soil 



9 



either in sacs, known as pycnidia (fig. 2, d) or on 
free stalks, known as conidiophores, meaning stalk 
bearing spores (fig. 2, e.). Fungi, like bacteria, de- 
pend on animals or plants for their food. Like bac- 
teria, they are differentiated into saprophytes and 
parasites. 

Relationship of Micro-organisms to the 
Fertility of a Soil 

Bacteriologists are continually engaged in discov- 
ering the possible function of numerous groups of the 
soil organisms. A recent exhaustive study * of Acti- 
nomyces, or thread bacteria, in the soil, for instance, 
seems to show that they serve to decompose grass 
roots, being more numerous in sod than in cultivated 
land. Other groups of bacteria undoubtedly per- 
form other important functions. 

The mere presence of friendly micro-organisms in 
the soil, however, would be insufficient to assure the 
welfare of our cultivated lands. These minute or- 
ganisms must find the conditions necessary to induce 
a maximum activity in th^ performance of their 
work, which is to act as chief cook in the dietary of 
the plant. Most of the plant's food, as it is found 
in the soil, is in a crude and unavailable form. The 
bits of mineral matter, the manure, or fertilizer 
added to the greenhouse soil, all contain plant 
foods, but in a form which plants cannot readily 

♦Conn, Joel H., New York (Geneva), Agr. Expt. Sta. BuL 52: 
3-11, 1916. 



10 Diseases of Greenhouse Crops 



use. They must be softened and predigested, and 
this work is done by the friendiy micro-organisms. 
The supply of plant food is therefore directly de- 
pendent on the work of these minute scavengers. An 
intimate relation exists between the higher and the 
lower form of plant life, the one depending on the 
other for sustenance. 

A. Number of Micro-organisms in Soil. In- 
vestigations by Waksman * and others clearly show 
that micro-organisms are present in soils everywhere 
(see Table I and fig. 2, b). 

It should be remembered that differences in the 
physical and chemical nature of the greenhouse soil, 
the sort of fertilizers used and the amount of tem- 
perature and moisture will all be important factors 
in determining the number of micro-organisms pres- 
ent. 

Nature and Function of a Healthy Soil Flora 

The function of a normal soil is to provide avail- 
able plant food. About 95 per cent of the weight of 
a growing plant is made up of carbon, hydrogen, 
oxygen and nitrogen. The remaining 5 per cent 
constitutes the mineral or the non-combustible part 
or ash of the plant. Carbon, hydrogen, and oxygen 
are absorbed in the form of carbonic acid and water; 
nitrogen is usually derived from nitrates produced 
by micro-organisms out of organic matter in the soil. 
Neither the organic nor the mineral elements are in 

♦Waksman, L. A., Soil Science, 3: 565-589, 1917. 



The Healthy Soil ii 



Table i 







Actinomyces 


Fungi 


Source of Soil Used 


Bacteria 


or Thread 




Bacteria 




7,202,000 


711,000 


313,000 




8,257,000 


611,000 


375,000 




10,133,000 


900,000 


925,000 


New Jersey forest 


2,088,000 


1 20,000 


218,000 




2,600,000 




150,000 


Milltown bogs 


185,000 




33,000 


Buckalew bogs 


450,000 


12,000 


43,000 




220,000 


281,000 


113,000 




10,000,000 


2,000,000 


119,000 


California fertilized 


3,840,000 


680,000 


108,000 


California unfertilized 


6,444,000 


356,000 


36,000 




7,900,000 


1,400,000 


400,000 


Oregon white land 


3,400,000 


300,000 


300,000 


Porto Rico soil 


2,140,000 


960,000 


300,000 




2,070,000 


933,000 


30,000 


North Dakota flax 


1,730,000 


263,000 


23,000 




4,335,000 


665,000 


76,000 




6,035,000 


566,000 


330,000 




2,125,000 


574,000 


30,000 




2,440,000 


1,560,000 


230,000 


Maine Aroostook loam 


4,650,000 


250,000 


85,000 


Maine Aroostook infested. . . , 


15,000,000 


2,200,000 


300,000 




1,600,000 


1,100,000 


112,000 



12 Diseases of Greenhouse Crops 



a form which plants can use. They must at first be 
acted upon by certain definite micro-organisms in the 
soil. 

A. The Transformation of Carbon. Cel- 
lulose, which is but a form of carbon, consti- 
tutes a large per cent of the woody tissue of plants. 
Soils contain large amounts of cellulose and this un- 
doubtedly helps to maintain their proper physical 
condition. It is found in large quantities in straw, 
manure, or in green vegetable matter. But because 
of its complex form, plants cannot make use of it, 
until it undergoes a certain decomposition. This 
is accomplished by a group of soil bacteria known as 
Amylobacter, which, feeding on the dead vegetable 
cellulose, break it up, and reduce it to carbon dioxide, 
hydrogen and fatty acids. The carbon dioxide 
either returns to the air to replenish the atmospheric 
supply, or it unites with water to form carbonic acid 
and soil carbonates. The carbon dioxide is taken 
by the plants either directly from the air through 
the leaves, or from the soil in some carbonate form. 
Thus we see that it is not the cellulose nor the prod- 
uct of its decomposition that furnishes plant food, 
but certain inorganic elements which are set free 
in its decomposition. , 

B. Elaboration of Available Nitrogen. 
From the viewpoint of plant nutrition, nitrogen is 
unquestionably the most important of all elements. 
The nitrogen of the air, although totaling about 79 
per cent of it, is not in an available form. In the 
transformation of proteids into available nitrogen in 



The Healthy Soil 



13 



the soil, three definite processes take place, all thanks 
to the work of certain soil micro-organisms. 

1. Ammonification, In this process, the soil bac- 
teria attack the complex proteids and convert them 
into ammonia. The odor of ammonia from decom- 
posed urea, manure, or any other organic matter is 
always an indication that ammonification takes 
place. According to Sackett * and others the ability 
to bring about this change is attributed to the follow- 
ing soil bacteria: Bacillus mycoides^ Bacillus pro- 
teus vulgaris^ Bacillus mesentericus vulgatus^ Bacil- 
lus suhtilis^ Bacillus janthinus^ Bacillus coli commu' 
nis^ Bacillus megatherium^ Bacillus fluorescens lique- 
faciens^ Bacillus fluorescens putidus and Sarcina 
lutea. 

Recent investigations by Waksman f and others 
indicate that certain classes of fungi are even 
stronger ammonifiers than are bacteria. Trichoderma 
Koningi and the Mucorales fungi were found to be 
strong ammonifiers. Fungi, too, are very strong 
cellulose decomposers. Further extensive investiga- 
tions on soil fungi will no doubt more strongly es- 
tablish their relationship to ammonification. 

2. Nitrification. In order to be readily available 
for plants, ammonia and ammonia compounds must 
be changed still further into simpler compounds or, 
as the process is known, must undergo nitrification. 
The ammonia is first oxidized into nitrous acid and 
nitrates. This is accomplished by soil bacteria, Ni- 

♦Sackett, W. G., Colorado Agr. Expt. Sta. Bui. 196: 3-39, 1916. 
t Waksman, A., Soil Science 2: 103-155, 1916. 



14 Diseases of Greenhouse Crops 



trosomonas and Nitrosocoscus. The nitrates are then 
oxidized into nitric acid and nitrates, through the 
work of the bacterium, Nitrobacter. The nitrates 
are the only forms of nitrogen which plants can use. 

C. Action of Soil Flora on Mineral Sub- 
stances. Inert mineral substances, like the organic 
matter in the soil, must first be acted upon by cer- 
tain soil bacteria to be converted to a form which 
plants can readily assimilate. 

1. Changes of Phosphates. Phosphates as they 
commonly occur in nature are but little soluble in 
water. This is why they cannot be used in their 
first form, although they are required by most 
plants. Soils deficient in this element may be im- 
proved by such fertilizers as superphosphate of lime, 
ground bone, phosphate rock or Thomas slag. In 
the process of decomposition of organic matter a 
large quantity of carbon dioxide is liberated, which 
unites with the water in the soil to form carbonic 
acid. This acid attacks the insoluble phosphates, 
transforms them into superphosphates — the only 
form soluble in water, — and renders them available 
to plant life. 

2. Changes in Potassium^ Sulphur^ and Iron. 
The carbon dioxide and other organic acids pro- 
duced during the fermentation of organic mat- 
ter, attack the potash feldspar which occurs in 
the soil. The product is potassium carbonate 
which is soluble in water and hence readily taken 
up by plants. The nitric acid which is formed dur- 
ing nitrification may also combine with the raw pot- 



The Healthy Soil 



15 



ash in the soil, forming potassium nitrate which is 
a form available for plants. 

As a result of the activity of soil bacteria, hydro- 
gen sulphate is evolved from the decomposition of 
proteids. The sulphur may be further changed into 
sulphur dioxide, and when combining wdth water 
and oxygen, into free sulphuric acid. The latter 
readily combines with calcium or magnesium, form- 
ing calcium or magnesium sulphate, from which the 
plant obtains sulphur for the construction of its 
proteids. 



CHAPTER 2 



SICK SOILS 

When a soil is sick, either because its beneficial 
bacteria do not perform their functions properly, or 
because of abnormalities in its chemical or physical 
properties, careful treatment and proper cultural 
methods may restore it to health. But when a soil 
becomes sick and unproductive because parasitic 
forms gain a foothold in it, much greater skill and 
knowledge are required to cope with the problem. 
Its solution is of the greatest economic importance 
to the gardener and to the greenhouse man. 

Parasitic fungi, upon finding their way into a soil, 
do not necessarily interfere with the work of the 
beneficial bacteria, such as the ammonifiers and ni- 
trifiers, for instance. Nor do they always influence 
the chemical or physical nature of the soil. Many of 
them directly attack the crop itself, causing serious 
diseases in the plants. 

Damping Off 

This disease is 'very familiar to every grower of 
plants. It is peculiar to seedlings or tender plants, 
and is very prevalent in the greenhouse, the hot bed, 

l6 



Sick Soils 



17 



the cold frame as well as in the field. It is induced 
by the presence of definite parasitic fungi, which 
thrive best in overwatered soils, and when the green- 
house is kept at a comparatively high temperature 
with poor ventilation. Damping off is also favored 
by thick sowing and too much shade in the seed bed. 

Symptoms of Damping Of, Every experienced 
grower knows the disease when he sees it. Seed- 
lings freshly damped off are soft and water soaked 
at the base of the stem. If they are pulled they 
often break off easily. A more careful examination 
shows that the root system is entirely decayed, al- 
though the upper part of the stem and leaves may 
still be green, and also possibly fresh. The degree 
of prostration in the seedlings is determined by the 
amount of moisture in the soil. If it is slight, the 
seedlings will become flabby and wilted before they 
topple over. With a high moisture content, they 
are more firm, but become prostrate as soon as in- 
fection sets in. The trouble usually begins in spots 
in the bed, thence spreading in every direction. 
Damping off is usually caused by several fungi, the 
chief of which is Fythium de Baryanum Hesse. The 
organism was first named and described by Hesse in 
1874. Ward * found it to be a very prevalent para- 
site in the garden soils of Europe. In America the 
fungus was first recognized as of great economic im- 
portance by Atkinson. t The seedlings of most 

*Ward, M., Quart. Jour. Micros. Soc. New Ser. 22: 487, 
t Atkinson, G. F., New York (Cornell) Agr. Expt. Sta. Bui. 94: 
233-272, 1895. 



i8 Diseases of Greenhouse Crops 



greenhouse plants may become subject to damping 
off by Pythium. When examined under a compound 
microscope, Fythium de Baryanum is seen to be made 
up of coarse non-separate, highly granular, irregular- 
ly branched hyaline vegetative threads or mycelium. 
The younger growing threads are more finely granu- 
lar. The oldest are coarsely granular or more often 
empty. These threads penetrate the cells of the 
host, where they obtain its food. 

Pythium de Baryanum does not often fruit on 
the dead seedlings. The fmiting is better observed 
when the fungus is grown in pure culture. Under 
normal conditions it produces two forms of spores, 
conidia and oogonia. The summer spores, or co- 
nidia, are swellings formed at the tip of the hyphse 
(fig. 3, a.). These swellings readily break off from 
the mother threads and germinate by sending out 
a slender tube. This tube penetrates the seedling 
tissue where it grows and develops and after due 
incubation reproduces the disease. The oospore, 
or sexual spore, is the stage which is most commonly 
found. The female organ (oogonium) first devel- 
ops as a terminal enlargement which is cut off by a 
septum from the mother thread. Next or adjacent 
to it a slender tube is cut off from the mycelium by 
a septum. This tube performs the function of the 
male sexual organ and is known as antheridium. The 
latter then comes into close contact and empties all 
its content into the female oogonium (fig. 3, b and 
c). Fertilization thus takes place, and a mature 
egg, or oospore, or winter resting spore is formed. 



Sick Soils 



19 



The latest investigations have not yet disclosed 
whether or not Pythium de Baryanum is carried over 
from year to year by its oospores. It is apparently 
able to propagate itself indefinitely by its vegetative 
mycelium. 

Of the other fungi which are capable of pro- 
ducing a damping off in the greenhouse or seed bed 
may be mentioned Sclerotinia lihertiana Fckl., 
Phoma solani Halst., Colletotrichum sp., Fusarium 
sp., Sclerotium rolfsii Sacc. and Rhizoctonia solani 
Kuhn. Each of these, except the last, will be taken 
up separately in connection with the study of their 
respective hosts. 

The fungi which cause damping off are introduced 
into the greenhouse, primarily v/ith sick soil used in 
the compost, and also with infected manure. The 
practice of dumping diseased plants and all other 
infected material in the manure pile cannot be too 
strongly condemned. Sometimes very lightly infect- 
ed plants with no visible symptoms of disease in the 
seed bed may nevertheless act as carriers, and like- 
wise infect the greenhouse soil. 

Damping Off of Cuttings 

Greenhouse men are often troubled with a damp- 
ing off of cuttings. In specific cases this is brought 
about by parasitic fungi which, however, will be 
taken up at length under the discussion of the va- 
rious hosts. 



20 Diseases of Greenhouse Crops 



Root Rot 
Caused by Rhizoctonia solani Kuhn. 

Although not so virulent as Pythium, Rhizoctonia 
is a frequent cause of considerable failure in green- 
house culture. The fungus causes a damping off of 
seedlings and cuttings and a serious root rot. 

Symptoms, The symptoms of Rhizoctonia rot or ^ 
wilt do not differ materially from those produced by 
Fythium de Baryanum. On older plants, however, 
Rhizoctonia produces cankers or deep lesions which 
are very characteristic. These are formed on the 
roots as well as on the base of the stem. The lesions 
are reddish brown and extend into the cortical or 
vital layer as well as into the woody tissue. There 
is perhaps no other parasitic fungus which is so 
widespread and which is capable of attacking such 
a variety of hosts as Rhizoctonia. The work of 
Peltier * shows that the following greenhouse crops 
are susceptible to Rhizoctonia: beet, bean, cauli- 
flower, celery, cucumber, egg plant, horseradish, 
lettuce, muskmelon, pepper, radish, tomato, sweet 
alyssum, amaranthus, ornamental asparagus, china 
aster, begonia, candytuft, carnation, coleus, dianthus, 
lavatera, lobelia, pansy, poinsettia, sweet pea, violet. 

Cuttings of the following hosts are also reported 
by Peltier to damp off from Rhizoctonia : Abutilon 
hybridum, var. lavitzii, Acalypha wilkesiana, var. 

•Peltier, G. L., Illinois Agr. Expt. Sta., Bui. 189: 283-391, 1916. 



Sick Soils 



21 



bicolor, A. wilkesiana, var. tricolor; A. wilkesiana, 
var. marginata, Ageratum mexicanum, Alyssum odor- 
atum; Coleus, Cuphea phatycentra, Tresine, Petu- 
nia, Piguerua trinervia, Lautolina chamoecyparissus, 
Sedum spectabile, Althernanthera, Vincia major. 

The Organism, In the United States the first ex- 
tended account of Rhizoctonia was given by Pam- 
mel.* Many other excellent accounts by American 
workers have appeared from time to time, to which 
we shall have occasion to refer later. 

The genus Rhizoctonia includes several forms of 
sterile fungi, all of which are distinguished by the 
manner of growth in pure culture, and by its myce- 
lium. Young hyphse of R. solani Kuhn are at first 
hyaline, then deepening in color from a yellowish to 
a deep brown. The young branches are somewhat 
narrowed at their point of union with the parent 
hyphse and grow in a direction almost parallel with 
each other. A septum is also laid down at a short 
distance from the point of union with the parent 
mycelium (fig. 3, d and e.). There is another form 
of hypha which is made up of barrel shaped cells 
(fig. 3, f.), each of which is capable of germinating 
like a spore. In pure cultures R. solani produces 
sclerotia which are first soft, whitish, and which 
later become hard and dark. The fungus is, carried 
over from year to year as sclerotia which are able 
to withstand the effects of heat, cold, drought, or 
moisture. 

♦Pamrael, L. H., Iowa Agr. Expt. Sta., Bui. 15: 244-251, 1891. 



22 Diseases of Greenhouse Crops 



Parasitic Soil Fusaria 

Next in importance to Rhizoctonia is a group of 
fungi which belong to the genus Fusarium. Soils 
infected with these species of fungi become unfit 
for tomatoes, sweet peas, etc., thereby causing great 
financial losses to the greenhouse man. Individual 
difficulties will be taken up in studying each of these 
crops separately. As an illustration of a typical 
Fusarium sick soil let us consider the wilt of sweet 
pea. The cause of this trouble is a soil inhabiting 
fungus, Fusarium lathyri Taub. 

Symptoms. The first symptom of the disease is a 
sudden flagging of the leaves, accompanied by gen- 
eral wilting and collapse of the seedling. Usually 
upon sowing the seeds a fair percentage germinate 
and reach the height of about 8 to lo inches before 
they are attacked by the fungus (fig. 7, b.). If the 
collapsed seedlings are allowed to remain on the 
ground, the stems will soon be covered with the 
sickle shaped spores. Eventually the decayed tis- 
sue rots and is soon invaded by small fruit flies 
which now begin to distribute the fungus from place 
to place by carrying its spores. 

The Organism. The mycelium of Fusarium 
lathyri is hyaline, septate and branched. At an early 
age the mycelial cells round up into countless num- 
bers of chlamydospores. Old cultures are practically 
one mass of these resting bodies. The spores are of 
two sorts, the macroconidia which are sickle shaped, 



Sick Soils 



23 



3-4 septate, the microconidia are one celled, minute 
spherical to elliptical. 

Soils Rendered Sick by Certain Forms of 
Animal Life. Some soils are made sick by the 
presence of minute forms of animal life. A striking 
instance of this is the root knot, a disease produced 
by a little worm generally known as nematode, or 
eel worm. 

Root Knot 

Caused by Heterodera radicicola (Greef) Mull. 

Although root knot is most prevalent in light soils, 
it may sometimes be found in heavier lands. The 
trouble is most widespread out of doors in the South- 
ern States, where the winter is mild. In the North 
the worm is usually unable to winter over in the 
open unless it is protected by trash or dead weeds. 
It is, however, prevalent in greenhouses and is un- 
doubtedly introduced with sick soil brought in from 
the field. 

Symptoms. The disease is characterized by swell- 
ings or knots on the roots. These swellings may be 
variously shaped, and are often mistaken for the 
true nodules of legumes (fig. 22.). Infected plants 
become stunted, pale, and usually linger for a long 
time before d3ring. 

The Organism, The nematode is a very minute 
worm, seldom exceeding one twenty-fifth of an inch 
in length. It is semi-transparent so that it cannot 
be easily detected by the naked eye. In searching 
for the eel worm, it is necessary to break a fresh knot 



24 Diseases of Greenhouse Crops 

(fig. 4, a-e.). Close examination will reveal two 
types of worms; a spindle shaped worm, the male, 
and a pearly white pear shaped organism, the fe- 
male, firmly embedded in the gall tissue. The fe- 
male is very prolific, depositing no less than 400 to 
500 eggs during her lifetime. The eggs are whitish, 
semi-transparent, bean shaped bodies, and too small 
to be noticed without the aid of a magnifying glass 
(fig. 4, f.). The time which elapses until the eggs 
hatch (fig. 4, f-u) depends largely upon weather 
conditions. In warm days the eggs hatch sooner 
than in cold days. Upon hatching, the young larvae 
either remain in the tissue of the host plant in which 
they emerge, or, as is more often the case, leave the 
host and enter the soil. This is the only period 
during which the worms move about to any great 
extent in the soil, where they either remain for 
some length of time or immediately penetrate an- 
other root of the host. The nematodes in most cases 
become completely buried in the root tissue, estab- 
lishing themselves in the soft cellular structure which 
is rich in food. The head of the worm is provided 
with a boring apparatus consisting of a sharply 
pointed spear, located in the mouth. This struc- 
ture not only aids it in getting food but is also val- 
uable in helping the young worms to batter through 
the cell walls before becoming definitely located. 
The two sexes during the development are indis- 
tinguishable up to fifteen or twenty days, both be- 
ing spindle shaped. In the molting or shedding of 
the skin, there is a marked change in the case of the 




Fig. 4. Nematode. 

c. Very young, normal root, b. mature, normal root, d. young root same age, 
c. attacked by nematodes, d. same, one week later, e. section of mature gall, 
showing distortion of tissue, f-ii. the various stages of development of the young 
embryo worm, beginning with f, as the egg and ending with u as the mature 
worm ready to hatch (o-it after G. E. Stone and R. E. Smith). 



Sick Soils 



25 



female, especially in the posterior region of the 
body, which no longer possesses a tail-like appen- 
dage. Fertilization occurs soon after this molt, and 
many radical changes occur in the shape and struc- 
ture of the organization of the worm. The fer- 
tilized female increases rapidly in breadth and be- 
comes a pearly white flask or pear-shaped individual. 
At this stage it is far from being worm-like and 
may, therefore, be overlooked by one unfamiliar with 
the life-history of the eel worm. The young male 
is much like that of the young female larvse, being 
spindle shaped in outline. The male does not cause 
as much damage to the root tissue as the female, 
and its purpose in life seems to be only that of fer- 
tilizing the female, for after this function has been 
performed, it is quite probable that the male worm 
takes no more food. 

Omnivorous Nature of the Eel Worm. There are 
two hundred and thirty-five species of plants known 
to suffer from the eel worm. This number includes 
all the important families of the flowering plants. 
According to Bessey * the following are among the 
greenhouse plants subject to root knot: bean, beet, 
cantaloupe, cauliflower, cucumber, egg-plant, lettuce, 
radish, tomato. For methods of control, see p. 40. 

Leaf Blight Nematode 

Caused by Apkelenchus olesistus Rizema-Bos. 
Beside the root knot disease which is caused by 

♦Bessey, E. A., U. S. Dept. Agr. Bureau PI. Ind. Bui., 217: ^-%^ 
1911. 



26 Diseases of Greenhouse Crops 



Heterodera radicicola there is another nematode 
which confines its injury to foliage only. 

Of the greenhouse hosts affected by this pest may 
be mentioned the Begonia, Asplenium nidus-avis, 
Pteris serrulata avistata, Pteris wimeseth, Pteris 
tremula, and Pelargonium. 

Symptoms. On the Cincinnati begonia the symp- 
toms, according to Clinton,* are manifested as nu- 
merous small indistinct discolorations limited by the 
small veinlets. In time, however, the tiny spots en- 
large and unite, forming a conspicuous reddish-brown 
blotch. Frequently infection is manifested as long 
streaks along the main veins. Often isolated spots 
occur in the midst of the surrounding healthy tissue 
(fig. 5, a.). On Asplenium nidus-avis, the trouble 
becomes conspicuous in dark brown areas from the 
base of the leaf near the midrib. These spread up- 
ward until the entire lower half of the leaf is killed. 
On Pteris, the spots appear as reddish brown bands 
reaching out from the midrib to the border, but lim- 
ited side wise by the small parallel cross veins (fig. 
5,b.). 

The Organism, The nematode in question is a 
slender microscopical worm. The latter chooses the 
nir chamber of the leaf in which to lay its eggs and 
upon hatching travels around in different parts of 
the same leaf or to the neighboring foliage. The 
worm can travel only when there is a wet film on 
the leaves. 

•Clinton, G. P., Connecticut Agr. Expt Sta., Thirty-ninth Ann. 
Rept. : 455-462, 1916. 




Fig. 5. Leaf Blight Nematode. 

a. Infected begonia foliage, b. the blight on fern leaves (a-b, after Clinton). 



Sick Soils 



27 



Control. Immersing fern plants for five minutes 
in water heated to 122 degrees F. (50 degrees C.) 
does not seem to injure the ferns, but seems to kill 
the nematode. All infected leaves should be cut off 
and burned. Diseased plants should be isolated from 
healthy ones. Spraying with Bordeaux may also 
act as a repellant. 



CHAPTER 3 



TREATMENT OF SICK SOILS 

Our conception of a healthy soil as has been in- 
dicated is one which is ideally suited to plant growth, 
through proper physical and chemical make-up, and 
by the presence of groups of beneficial micro-organ- 
isms. A sick soil is one in which plants would grow 
very languidly or not at all. Soil sickness may be 
caused through the improper use of fertilizers, or 
through the introduction of parasitic disease-produc- 
ing organisms. 

Acid-Sick Soils 

Soils which contain an excess of acid, in which 
crops refuse to grow, may be termed acid-sick. Acids 
in soils have a directly poisonous effect on plants. 
Soil acidity may be brought about by the loss of lime 
and of other bases; and by the decomposition of 
organic and of inorganic matter. 

Crops are known to draw heavily on the lime 
of the soil, and thus to increase the proportion of 
acidity. This, then, is one direct way of depleting 
the soil lime. Lime and other bases are further 
lost from the soil by leaching. The soluble car- 
bonates are but slowly soluble in pure water. How- 
ever, carbon dioxide, nearly always present in soils, 

28 



Treatment of Sick Soils 



29 



changes the calcium carbonate into calcium bicar- 
bonate, which is very soluble, and readily leaches 
out with the drainage water. 

Soils which are heavily manured are apt to be- 
come more acid. The decomposition of the organic 
matter yields large quantities of carbon dioxide 
which act on the carbonate in the manner above in- 
dicated. In addition to these causes, poor drain- 
age has a tendency to increase the soil acidity. The 
application of ammonium sulphate as a fertilizer 
leads to a development of acidity by the production 
of sulphuric acid. The same is true when other 
acid fertilizers are used. In the process of nitrifi- 
cation, in which nitrogen is made more available for 
plants, acids are produced. Acidity in a soil is 
usually characterized by a languid condition of the 
growing crop. This may be due directly to the 
effect of the acid on the plants, or to the inhibiting 
effect of the acid on the soil flora. In the latter case 
the plant food in the soil, although very plentiful, 
may not be in a form available for plants. 

Not all crops are equally sensitive to soil acidity. 
Hartwell and Damon* have determined the degree 
in which truck crops are benefited by the application 
of lime to an acid soil. Those which are very sen- 
sitive to soil acidity are followed by the number 
(3), while a lesser degree of sensitiveness is indi- 
cated by the numbers (2) and (1). Crops which 
tolerate a moderate amount of acidity are followed 

*Hartwell, B. L., and Damon, S. C, Rhode Island Agr. Expt 
Sta. Bui. 160: 408-446, 1914. 



30 Diseases of Greenhouse Crops 



by the figure (o), and those which thrive best in 
acid soils ( — i); beans (o), beets (3), carrots (1), 
cauHflower (2), celery (3), cucumber (1), egg- 
plant (2), lettuce (3), muskrnelon (o), parsley (o), 
pea, garden (1), pepper (3), radish (1), rhubarb 
(3), sorrel (—1), spinach (3). 

Treatment of Acid Soils 

The best known remedy for soil acidity is lime. 
Its effect is to neutralize the acidity, and to restore 
the normal equilibrium for the activity of the soil 
flora, thus overcoming the antagonism to normal 
growth. The amount of lime to be used depends on 
the kind of soil, its degree of acidity, and the crops 
grown. It is very unlikely that injury would result 
to greenhouse crops from the use of moderate 
amounts of lime. Lime is sold as ground limestone 
or as burned lime. A ton of burned limestone will 
yield 1,120 pounds. If enough water is added, it 
will weigh 1,480 pounds. If 1,120 pounds of 
burned lime or the 1,480 pounds of hydrated lime 
are allowed to air slack, the weight of both will be 
2,000 pounds. Air slacked lime has the same com- 
position as ground limestone. In buying hydrated 
lime we do not get any better quality, but merely 
pay an excess in freight for the amount of water it 
contains. The cost of delivery should determine the 
kind of lime to buy. 

Wood ashes may often be used instead of lime 
to correct soil acidity. Hardwood ashes contain 
about 30 per cent, lime and 60 per cent, potash. 



Treatment of Sick Soils 



31 



Two and a half tons of good wood ashes are equiva- 
lent to one ton of burned lime for overcoming soil 
acidity. Leached ashes have lost their potash and 
its lime is in the form of a hydrate or carbonate. 

Magnesium lime, which contains a high percent- 
age of magnesia, is not objectionable for use. In 
fact, a ton of limestone, which contains magnesium 
carbonate is more effective on acid soil than a ton 
of limestone without magnesium carbonate. Lime 
should be applied only when the acidity of the soil 
requires it. 

Alkali Soils 

Alkali soils are termed sick, since plants thrive 
there poorly or not at all. The alkali problem gen- 
erally concerns only those greenhouse men located 
in the irrigated districts of the arid or semi-arid 
regions of the United States. 

For convenience, alkali soils are here divided into 
black and white. The black alkali lands are known 
to contain sodium carbonate or washing soda as the 
essential salt. The latter does not act so much on 
the soil as on the organic matter, turning it black. 
This dark material is always found on the surface 
with the salts. The blackening of the soil, however, 
is not always an indication of black alkali. Many 
dark spots are found to contain the white alkali. 
Moreover, soils which contain little or no organic 
matter may contain large quantities of sodium car- 
bonate and never turn black. The white alkali in 
reality is not a true alkali. The salts found in it 



32 Diseases of Greenhouse Crops 



are sodium chloride or table salt, calcium sulphate 
or gypsum, sodium sulphate, magnesium sulphate or 
epsom salt. In addition to these may be found 
salts of potassium. 

Methods of Control. Generally speaking the al- 
kali problem is not serious in greenhouse culture. 
The alkali soil when mixed at the compost heap 
generally loses much of its salts due to the action 
of the manure used. However, in alkali regions 
alkali soils should be avoided as much as possible. 
When this is not possible the soil to be used with 
the compost should be spread out and exposed to 
the action of winter weather conditions and to the 
washing by rain. This treatment will result in a 
loss of the injurious salts through leaching. 

Soil Sterilization 

Damping off, whether induced by Pythium, Rhi- 
zoctonia or any other parasitic organism, is usually 
confined to seedlings in the seed bed under cover or 
in the open. The loss of seedling not only means 
a waste of seeds, but it also results in poor stands. 
The disease-producing-organisms are usually brought 
in with the manure and the compost. Most growers 
are in the habit of using the same soil in the seed 
bed or in the greenhouse year in and year out. A 
number make it a practice to empty their beds and 
use fresh soil every year. This, however, is too 
expensive and, moreover, is not always a safe 
method, for the new soil, too, may be contaminated, 
or may become infected as soon as it is placed in the 



Treatment of Sick Soils 33 

bed previously contaminated. Fortunately, sick 
soils in the greenhouse, unlike the soil outdoors, may 
be readily treated so as to destroy all forms of para- 
sitic micro-organisms or injurious animal life which 
are present in it. The various methods to be men- 
tioned make it possible to use the soil over and 
again. Rid the soil of parasites, then all chances 
will be in favor of good crops whether vegetables 
or flowers. 

Soil Treatmentt with Formaldehyde 

When steam sterilization is not feasible, because 
of the absence of suitable steam pressure, the for- 
maldehyde treatment is the next best. With this 
method we may control Fusarium, Rhizoctonia, and 
Fythium in infected beds. It is doubtful, however, 
if it will entirely eradicate eel worms from infested 
soils. The method is as follows : the beds are thor- 
oughly prepared in the usual way with all fertilizers 
worked in and then the soil is drenched with a solu- 
tion of formaldehyde composed of one pint of the 
chemical (40 per cent, pure) to 30 gallons of water 
applied at the rate of one gallon per square foot. 
The solution should be put on with a watering can 
and distributed as evenly as possible over the bed, 
so as to wet the soil thoroughly to a depth of one 
foot. It will, in most cases, be necessary to apply 
the solution in two or three intervals, as the soil 
may not absorb the full quantity of the liquid at 
one time. After treatment the beds should be cov- 



34 Diseases of Greenhouse Crops 



ered with heavy burlap to retain the foronaldehyde 
fumes for a day or two, and then aired for a week 
before planting. Stirring the soil at frequent inter- 
vals after uncovering hastens the more rapid escape 
of the formaldehyde fumes. 

Sterilizing Soils with Steam 

Steam sterilization of soils is by far the best 
method. There are four ways of steaming soils: 
(l) Inverted pan method, (2) the perforated pipe 
system, (3) the steam rake device, (4) the drain 
tile method. The choice of any one of these methods 
is a matter of expediency. All four methods have 
been successfully used on a commercial scale. 

The Inverted Pan Method, This was first devised 
by A. D. Shamel of the U. S. Department of Agri- 
culture. To carry it out, the boiler must maintain 
a pressure of not less than 80 pounds, for at least 
one and a half hours. In setting a pan, the rim is 
sunk into the soil of the seed bed or bench, to a 
depth of two to three inches, to make the inclosed 
chamber steam tight. In heavy soil, trenching may 
be necessary. It is also advisable to put a heavy 
weight on the pan when the steam operates. For 
one pan, a traction engine or a portable boiler of 
ten to twelve H. P. will suffice. While the standard 
of the pan is six by eight feet, the dimensions may 
be modified to suit the seed beds or greenhouse 
benches. 



Treatment of Sick Soils 35 



Selby and Humbert* describe the method of con- 
structing an inverted pan as follows : 

"Material used for construction of a pan is gal- 
vanized sheet iron ; the most useful weight is No. 20 
gauge, which weighs 26.5 ounces per square foot. 
The heavier material requires little in the way of 
frame supports. The galvanized iron sheets come 
in sizes vary^ing from two to three feet in width by 
eight to ten feet in length. The standard is a pan 
6x10 feet in area, six inches deep, constructed from 
5 such strips x 8 feet in size. These sheets arc 
joined by double fold seam and riveted at inter- 
vals of 6 to 10 inches to make the pan steam tight. 
This pan is further strengthened by a band of strap 
iron 2x1 inch riveted to the bottom edge, and 
stiffened by a brace of ij^'ii^ch angle iron across 
the top and extending down the sides. This is 
bolted at the sides to the supporting strap iron 
stiffener. 

''The entrance pipe for the steam may be placed 
at the side or end of the pan or may enter from the 
top. The latter form has the advantage in that it 
will not interfere with the box boards when used 
on frames. The pipe, after entrance, should be a 
T form, so that steam in being forced into the pan 
when in place does not blow holes in the soil." 

The pans, together with the sand bags used for 
weight, are mounted on a frame which rests upon 
wheels. The wheels run on the edges of the con- 

♦Selby, A. D., and Humbert, J. G., Ohio Agr. Expt. Sta. Circ. 
151: 65-74, 1915. 



36 Diseases of Greenhouse Crops 



Crete walks on either side of the house. By using 
a pulley, the pan may be conveniently placed 
wherever desired. 

Perforated Pipe Method. The apparatus consists 
of a set of perforated pipes buried in the soil and 
connected with a steam boiler. The main and cross- 
head pipes are 2 inches and those which are buried 
ij^ inches. The length of the beds, and especially 
the capacity of the boiler, will determine the num- 
ber of pipes to use. However, 7 to 8 pipes are as 
many as could be used to advantage. These should 
not be over 40 feet long. The perforations should 
be one-eighth to three-sixteenths of an inch in size, 
12 to 15 inches apart and on the upper side of the 
pipes. The latter are buried about six inches deep 
and when the steam is turned on the beds are cov- 
ered with a heavy canvas to retain the heat and to 
prevent the escape of steam (fig. 6, a and b.). When- 
ever convenient, it is well to have two sets of pipes 
so as to save time and fuel. 

Steam Rake Method, This consists of a two-inch 
main pipe which may be run between two sets of 
houses. The pipe is connected with the boiler at 
one end and with a heavy hose at the other. The 
rake is attached to the hose through which the steam 
is introduced. There are either two rakes used in 
a single house, or four rakes operated in pairs, end 
to end in two adjoining houses. The rake is gener- 
ally composed of three main pipes 13 feet long, 
which run crossways of the house, and of several 
cross pieces one inch in diameter that are gradually 




b 



Fig. 6. 



a. Steam sterilization apparatus, b. bed ready to be ster- 
ilized, showing steam connection and burlap covering. 



Treatment of Sick Soils 37 



reduced to three-fourths inch, then to one-half inch, 
then to three-eighths inch. The pegs are six inches 
long, and are placed eight inches apart, and consist 
of one-fourth inch pipe pounded together at the 
lower end. The steam escapes through a three- 
sixteenths inch hole at the lower wedge-like end of 
the pipe. The advantage of this apparatus is that 
it can be made to fit any bed. At 90 to 100 pounds 
pressure, more steam will naturally pass through 
the pipes than at thirty to forty pounds pressure. 
During the operation, a canvas cover laid on the 
beds will prevent the rapid escape of steam. 

The Tile Method. This system is at its best when 
the steam pressure is low, at 25 to 30 pounds. With 
higher pressures the steam will blow out between 
the tiles. With this method, therefore, the soil 
should be sterilized for a longer period of time, 
from two to four hours, depending on the depth of 
tile and on soil conditions. Usually the tiles are 
not laid over one foot deep and from two to three 
feet apart. The joints of the pipes should be well 
matched. 

Hot Water Sterilization, Numerous greenhouse 
men seem to prefer the use of hot water as a soil 
sterilizer to any other method here mentioned. Mr. 
Wm. L. Doran of the Massachusetts Experiment 
Station, who has made considerable study of this 
method, writes as follows : 

''The soil should be thoroughly dry in the begin- 
ning so that it will take up the maximum amount 
of water. Before treatment, it is spaded over to 



38 Diseases of Greenhouse Crops 



a depth of one foot to insure an open, porous con- 
dition. The water is heated in an ordinary boiler 
such as is used for heating the greenhouse, no extra 
equipment being needed. It is moved by a small 
pump operated by a motor and gasoline engine of 
a small horse power. The water comes out under 
forty pounds pressure, which insures considerable 
penetration into the soil. It is piped from the boiler 
through the center of the greenhouse in i^-inch 
iron pipes. Most growers take the water from the 
bottom of the boiler rather than from the top, the 
object being to keep the temperature high but to 
avoid the steam which is objectionable. A ther- 
mometer is screwed into the main outlet pipe and 
is read frequently; the temperature should be above 
201 degrees F., but if it goes much above 215 de- 
grees F. the outlet pipe spits steam and is difficult 
and dangerous to use. To this iron pipe in the cen- 
ter of the house is attached a one-inch rubber hose 
fifty feet in length. This hose is replaced annually 
to decrease the danger of blow-outs and burns. 
Most growers sterilize once a year, some twice. The 
rubber hose is attached at the other end to a Y 
joint which is in the middle of a five-foot iron pipe 
one inch in diameter. The upper half of this pipe 
is plugged at both ends, serving simply as a handle, 
and from the lower half the water is delivered to 
the soil. A few feet back of this exhaust pipe the 
rubber hose is wrapped with burlap so that it may 
be carried over the shoulder of the workman. Some 




Fig. 7. Effect of Soil Sterilization. 

a. To left, sterilized soil planted in sweet 
peas, to right Rhizoctonia sick soil unsterilized 
and where seed failed to germinate. b. To 
left, sterilized soil planted in sweet peas, to 
right. Fusarium sick soil unsterilized, where 
seed failed to germinate. 



Treatment of Sick Soils 



39 



growers shove the iron pipe down into the soil six 
inches; others hold it above the surface of the soil. 
The water penetrates equally well either way, be- 
cause the soil is in a loose condition and the water 
goes out under pressure. There are no figures as to 
the exact amount of water per cubic foot of bed sur- 
face, but hot water is applied until it stands on the 
surface of the soil in pools and will no longer pene- 
trate. The exact amount will, of course, vary with 
the physical condition of the soil and its relative 
dryness. The greenhouse men do not practice cover- 
ing the soil with anything to hold in the heat. 
Out of doors, however, a cover would be desirable 
because of wind currents. Three or four days after 
treatment, the soil is cool enough and dry enough 
to plant." 

It will require about two days for five men to 
treat a house 275 feet by 34 feet. 

Roasting or Fan Firing. By this method, the 
soil to be sterilized is removed from the bed and 
placed in a pan, over a hot fire. After roasting, 
the soil is returned to the bed and more of it steril- 
ized. This method is too slow and has the disad- 
vantage, besides, of destroying the humus in the 
soil. The advantage of steam sterilization and of 
the ''fire" methods lies in the destruction of all 
weed seed, together with the fungi which cause 
damping-off (fig. 7, a and b.). 



40 Diseases of Greenhouse Crops 



A New Method of Steam Sterilization for 
Controlling Nematodes* 

It has been our common experience, when at- 
tempting to control nematodes by steam steriliza- 
tion of the soil, that very frequently one is unable 
to secure sufficient steam pressure satisfactorily to 
use the common harrow-type of sterilizer, the in- 
verted pan or any modification of these types. 
When the steam pressure is only 50 to 60 pounds 
or less at the boiler, and where it becomes necessary 
to carry this a considerable distance in the green- 
house, condensation takes place, and as a result 
these sterilizers cause puddling of the soil and other- 
wise inefficient work. In our experiments, all modi- 
fied types of steam sterilizers which originated from 
those already mentioned were equally unsatisfac- 
tory; therefore, a method which could utilize a low 
steam pressure and still do good work without in- 
jury to the soil, seemed urgent. 

The method to be described herewith was used 
in a span of fifteen greenhouses, which had the soil 
badly infected with nematodes. For two successive 
seasons previous to the treatment of the soil, the 
entire crops of tomatoes and cucumbers were a total 
loss. After unsuccessfully trying out all styles of 
steam sterilizers, the device herein described was de- 
vised and proved successful. 

It should be remembered where 80 pounds or 

*By L. E. Melchers, Kansas State Agricultural Experiment 
Station. 



Treatment of Sick Soils 



41 



more pressure is obtainable, the aforementioned 
kinds of apparatus may give very good results, but 
where the pressure is less, as in many cases in steam 
heated plants, they are not satisfactory. 

The necessary equipment for this new device con- 
sists of two 2 X 4's cut at suitable lengths, a few 
boards either the entire length or half the length 
of the width of the greenhouse, canvas, burlap, 
sacking or tarpaulin. This method has been devised 
purposely for greenhouses growing vegetables on 
the ground, although modifications of this method 
could be made to suit other conditions. 

The first operation in carrying out the work con- 
sists of digging a pit at one extremity of the house 
to the depth that one wishes the soil sterilized. The 
width and length depend somewhat upon the width 
of the greenhouse. In our work the pits were dug 
12 inches deep, 6 to 8 feet wide and lo to 15 feet 
long. Two 2 X 4's are laid on edge in the bottom 
of the pit. These pieces should be the length of the 
pit and placed about 6 to 12 inches from the sides of 
the pit. One or two leads of steam pipes with T out- 
lets in the center and at the ends of the pipes should 
be laid in between these two stringers (2 x 4's). The 
pipes can best be run in from the ends of the pits. It 
has been found better to let the steam out in large 
quantities and not through perforated pipes. Pieces 
of 2 X 4's are then laid across these two stringers and 
should be long enough to reach across the width of 
the pit. Quite a large number are necessary to form 
a kind of platform. About a quarter of an inch 



42 Diseases of Greenhouse Crops 



should be left between the 2x4 cross pieces to allow 
for the ascent of the steam (fig. 8, a, b, c). 

When the bottom has been laid, the soil which 
was removed can be thrown onto the platform. 
Boards should be staked around the sides of the 
platform to retain the soil. This forms a kind of 
wagon box. The steam can then be turned on, ther- 
mometers placed in the soil and the entire pit cov- 
ered with any suitable covering to retain the heat. 

Since steam rises, this method is much more satis- 
factory than where it becomes necessary to force the 
steam downward. There is no puddling of soil, 
even at the lower pressures, and 212 degrees F. and 
higher temperature can be obtained when steriliz- 
ing 12 inches of soil. It should be remembered 
that a few inches of soil below the wooden platform 
is likewise sterilized in this process. The skeleton 
platform is easily removed by means of an iron bar 
with a hook at the end for catching hold of the 
2x4's and jerking them from underneath the soil. 
When the framework has again been set and the 
steam pipes adjusted in place, the platform is ready 
for the second batch of soil, which is dug immedi- 
ately adjoining the soil which was just sterilized. 
In order to avoid extra labor, it becomes necessary 
to have one pit already dug just ahead of the bed 
being sterilized, so when the 2 x 4's are removed 
they can be laid immediately in the pit which i$ 
ready for them. This is accomplished by erecting 
the second bed on top of the first one, i.e., on top 
of the soil just sterilized. 



c 



Fig. 8. Melcher's Soil Sterilizer. 

a. The 2x4 bottom laid and ready for the soil, b. 
bed ready for steaming, c. steaming the soil in two beds 
running the width of the greenhouse. 



Treatment of Sick Soils 43 



When the second bed is ready for sterilization 
(it is directly on top of the one first sterilized)^ one 
has a pit already dug to set the framework in for 
the third batch, and from hence on, a pit will always 
be in readiness for the framework. It will be seen 
by this process and by such procedure that it be- 
comes necessary to return one batch of sterilized 
soil to the opposite end of the greenhouse, after the 
whole house has been sterilized. This is the second 
batch, which was sterilized and sets on top of the 
first. This cannot be avoided, but the soil can easily 
be carted back by means of wheelbarrows. 

Many greenhouses are irregularly constructed, 
with uprights and other obstructions more or less 
promiscuously scattered; therefore, the pan method 
is often difficult to use and it is less easy with the 
other unadjustable apparatus, but with the method 
just described these obstructions are much less seri- 
ous, since they can be allowed to come in any part 
of the bed without hindrance to sterilization. 

There is a little more expense connected with this 
method, on account of extra labor which is neces- 
sary, but this method is not being advocated as a 
superior way of steaming the soil, but rather to do 
the work where situations arise that cannot be han- 
dled otherwise. 

Effect of Soil Sterilization on Seed Germination, 
The main object in sterilizing soils is to destroy the 
harmful fungus flora. Of all the methods here 
recommended, steaming is the most effective. Not 
all soils, however, are alike benefited by this treat- 



44 Diseases of Greenhouse Crops 



ment. With lettuce seed, for instance, there is a 
higher per cent, of germination usually obtained in 
the sterilized soil. With tomatoes, however, ger- 
mination is retarded under similar soil treatment. 
On the average, germination is favored by soil ster- 
ilization. This is well shown in Table 2.* 



Table 2 



Kind 

of 
Seed 


Total 
Number 

of 
Seed 
Tested 


NU7 

Germin 

Steril- 
ized 
Soil 


nber 
ated in 

Unsteril- 
ited 

Soil 


Per 
Cent. 
Gain 

or 
Loss 






6oo 


159 


81 


41 






6oo 


93 


no 


13 


Cucumber 




6oo 


281 


187 


33 






6oo 


26 


10 


61 






6oo 


37 


33 


10 






400 


48 


31 


35 


Mustard. . 




400 


84 


33 


61 






400 


105 


37 


64 






200 


57 


33 


43 






200 


87 


26 


70 



Effect of Soil Sterilization on Plants. That soil 
sterilization is practicable cannot be doubted. With 
some crops, the beneficial effect is especially marked. 
The Massachusetts Experiment Station t found a 
considerable increase in the production of violet 
blossoms as a result of soil sterilization. This is 
well shown in Table 3. 

♦From the Massachusetts Agr. Expt. Sta., 15th Rept.: 40-42, 1903. 
t Massachusetts Agr, Expt. Sta., 12th Ann. Rept.: 165-167, 1900. 



Treatment of Sick Soils 45 



Table 3 



Date 


No. of Blossoms Picked 


Percentage 


Unsterilized 


Sterilized 


uatn 




Soil 


Soil 






19 


38 


100 




62 


lOI 


63 




55 


125 


127 




39 


72 


84 




144 


250 


73 




482 


510 


5 


Total 


801 


1,096 






133 


182 


'36 



Not only was production of flowers increased in 
the sterilized soil, but there was also a decided de- 
crease in leaf spots. 

Changes in the Soil due to Sterilization, Vari- 
ous investigators have found that by steam heat- 
ing, the physical, chemical, and physiological prop- 
erties of a soil are more or less changed. Through 
chemical action there is an increase of soluble mat- 
ter in some of the inorganic substances such as pot- 
ash and phosphoric acid as well as in the organic 
matter. Ammonia is also formed by the reduction 
of nitrates to nitrites and by the decomposition of 
organic compounds, large amounts of which are also 
made available for plant growth. This, then, would 
explain the reason of the stimulation of growth in 
sterilized soils. However, steamed soils may also 
contain injurious substances, which upon becoming 
soluble are harmful to plant growth and to the ger- 
mination of certain seed. This seems especially the 



46 Diseases of Greenhouse Crops 



case in steamed soils deficient in lime. The inves- 
tigations of Schreiner and Lathrop* have shown 
that as a result of heating, dehydroxystearic acid is 
produced, and that this is harmful to plant growth. 
Heating soil produces both beneficial and harmful 
substances. The fertility is raised or lowered, de- 
pending on which of these predominates. The re- 
sult, however, is influenced by the crop, the fer- 
tilizer used, and the amount of lime applied. Cole- 
man t has found that intermittent sterilization by 
means of dry heat at 82 degrees C. for five suc- 
cessive days in moist soil produced but very slight 
chemical changes. But this slow method is not very 
popular with the grower. Since, however, sterilized 
soils lose their harmful substances by standing, the 
treatment of the soil during the summer months, 
when there is no crop in the greenhouse, will obvi- 
ate the main difficulty. 

Other Methods of Controlling Damping Off, 
Damping off may be largely controlled by careful 
cultural conditions. Unless the soil of the seed bed 
has been sterilized, it is unwise to use the same 
soil in the beds where damping off has occurred 
previously. Thick sowing, too, should be avoided. 
In Table 4, Johnson + presents some interesting data, 
showing the effect of thick sowing on damping off. 

*Schreiner, O., and Lathrop, E. C, U. S. Dept. of Agr., Bur. 
of Soils, Bui. 89: 7-37, 1912. 

t Coleman, D. A., et al., Soil Science: 259-274. 1916. 

t Johnson, James, V^isconsin Agr. Expt. Sta., Research Bui. 31: 
31-61, 1914. 



Treatment of Sick Soils 47 



Table 4 



Flat NuriibcT 


Weight of Seed Sown 


Plants 
Diseased 


Per 
Flat 


Per 100 
Square Feet 




Grams 
0. 1 
0.2 

0.3 
0.4 

0.5 
0.6 
0.7 
0.8 
0.9 

1.0 


Ounces 
0. 16 

0.33 
0.49 
0.66 
0.83 
0.99 
1. 16 
1-33 
1.49 
1.60 


Per Cent. 

0 

0 

8 
15 
35 
75 
80 
80 
92 
96 


2 


3 


4 


5 


6 


7 


8 


9 







Certain soils are especially favorable to damping 
off. Soils which contain a higher percentage of 
unrotted vegetable matter, and those which are hard 
to drain need special attention. Great care should 
be taken to keep the seed bed at the right tempera- 
ture. The latter cannot be guessed at by personal 
sensation. It should be accurately determined by 
thermometers placed in the bed at suitable distances. 
It should also be remembered that any covering 
cloth or sash will exclude light and air. Every 
precaution should, therefore, be taken to prevent 
the seedlings from becoming "drawn," for in that 
condition they are most susceptible to damping off. 
The safest plan is to keep the temperature a trifle 
lower than is generally required, and to allow as 
much ventilation as possible. Very often damping 
off starts only in one corner of the bed. To check 
the rapid spread of the disease, the infected area 



48 Diseases of Greenhouse Crops 



may be removed. Spraying the seedlings with vari- 
ous fungicides in a bed where damping off has be- 
come well established will be of little help. 

Control of Insect-Infested Soil, Spraying the 
soil will be of little value in the control of under- 
ground insect pests. Fortunately, however, there 
are other means of dealing with them. All insect 
pests may, of course, be controlled by steaming the 
soil in the benches. 

Cut worms may be controlled by the use of a 
poisoned bran made as follows : To three ounces of 
molasses add one gallon of water and sufficient bran 
to make a fairly stiffened mixture. To this add 
a teaspoonful of Paris green or arsenic and stir 
well into a paste. A heaping teaspoonful of the 
mixture is scattered here and there over the infested 
bed. The cut worms will be attracted to the sweet- 
ened bran and after eating it will die from the 
poison. 

Summer Treatment of Greenhouse Soil 

The greenhouse is rarely used the whole year 
round. During the summer the house is usually 
idle one or two months. This is especially true re- 
garding truck crops, for at that time outdoor prod- 
ucts put the greenhouse out of competition. 

It is a common belief that if the soil is allowed 
to remain dry in the intense heat under glass dur- 
ing July or August all injurious insects, fungi and 
bacteria will be destroyed. To determine this point 



Treatment of Sick Soils 



49 



Green and Green* have carried out some interesting 
experiments. They used beds which had been 
treated as follows: New soil, straw mulch, manure 
mulch, and a summer soil, sun-dried soil, in the 
greenhouse. The results of these experiments with 
tomatoes are shown in Table 5. 



Table 5 



Plot 


1908 


1909 


1910 


1911 


1912 


1913 


Average 


New soil 


5-2 


4-5 


3.5 






3-3 


4.1 


Straw mulch 


4-9 


3-2 


31 






2.5 


3-4 


Manure mulch 


51 


4.2 


30 






2.6 


3-7 


Dry . 


2.6 


31 


2.1 






.9 


2.1 



It is seen from Table 5 that as far as tomatoes 
are concerned the new soil gave the best results. 
The manure mulch is second in productiveness. 
The effect of the dry mulch shows a rapid decline, 
and the dried soil showed the poorest yield. It must 
be added that in this soil the greatest amount of 
disease was present. 

The result obtained with the soil treatment of 
tomatoes was found to be different from that with 
winter lettuce. This is more clearly brought out in 
Table 6 (see next page). 

This table shows that the drying of the soil does 
not affect the lettuce crop to the same extent as 
it does tomatoes. Unlike most crops in the green- 
house, lettuce thrives best in old soil. On the other 
hand, cucumbers are as sensitive as the tomato to 

•Green, W. J., and Green, S. N., Ohio Agr. Expt, Sta., Bui. 
53-68, 1915. 



50 Diseases of Greenhouse Crops 



Table 6 



Plot 


1911 


1911-12 


1912 


1912-13 


Average 




324 


432 


3.33 


332 


3-55 


Straw mulch 


3.06 


301 


2.85 


300 


2.98 


Manure mulch .... 


3.74 


4.61 


4. II 


4.29 


4.18 


Dry 


3.29 


525 


3-86 


4.05 


4. II 



old, well manured soil in the greenhouse. This 
does not imply, therefore, that it is necessary to 
renew the soil every year for cucumbers or toma- 
toes. Soil sterilization, good drainage, and liming 
will tend to overcome the ill effect of old soils on 
these crops. 



PART II 
CULTURAL CONSIDERATIONS 



CHAPTER 4 



LIGHT IN ITS RELATION TO GREENHOUSE CULTURE 

Of the many factors which are intimately inter- 
woven with the growing of greenhouse crops, light 
is a very important one. Unfortunately, this sub- 
ject has received scant attention. However, Dr. 
Stone* of the Massachusetts Agricultural Experi- 
ment Station has contributed greatly to our knowl- 
edge on this subject. It is apparent from his work 
that success with greenhouse crops goes hand in hand 
with a thorough understanding of the light require- 
ments of plants. The problem of light has a direct 
bearing on the physiology and pathology of hot- 
house crops. 

Physiological Relationship of Light 

To realize the importance of this subject we must 
be aware that nearly ninety-five per cent, of the 
substances contained in the plant is derived from the 
atmosphere. These substances are manufactured 
through the action of light on the green matter 
(chlorophyll) located primarily in the leaves. This 

♦Stone, G. E., Massachusetts Agr. Expt Sta. Bui. 144; 3-39, 
1913- 

53 



54 Diseases of Greenhouse Crops 



process is known as photosynthesis. It consists of 
an intake and assimilation of carbonic acid by the 
plant, and a simultaneous liberation of oxygen. 
The carbonic acid breaks down and combines with 
the water to form the sugars and starch. The spec- 
trum rays which are most concerned with the manu- 
facture of starch are the orange and the red. The 
blue rays affect growth. Success with greenhouse 
plants depends largely on the intensity and the na- 
ture of the light rays which are permitted to pene- 
trate through the glass. At best, these rays differ 
materially from the normal sunlight. 

Contrary to general belief, plants make most 
growth at night or in the dark. On the other hand, 
photosynthesis takes place during the daytime and 
under the direct influence of light. While light docs 
not favor growth, it assists in the development of 
supportive tissue which enables the plant to resist 
attacks of various diseases. The lack of a proper 
amount of light in the greenhouse causes the plants 
to possess little or no resistance to disease. This is 
especially true in the winter months. However, 
while insufficient light is conducive to disease, an 
excess of it, such as occurs in the summer months, 
is also detrimental to plant health in the hothouse. 
In that case, shading the glass becomes necessary. 
Moreover, there are numerous hothouse plants, such 
as palms for instance, which naturally require less 
light. On the other hand, lettuce, tomatoes, cucum- 
bers, roses or carnations require more light in the 



Light in Greenhouse Culture 55 



winter months than the ordinary hothouse is able 
to furnish. 

Pathological Relationship of Light 

While it is true that plants grow in the dark, they 
must have light to thrive. The growth made in 
darkness exclusively is of a soft nature. The long, 
whitish, slender sprouts of potato kept in the dark 
are a good illustration. Numerous diseases of plants 
grown under glass may undoubtedly be traced to 
improper light conditions. Cucumbers, for instance, 
when grown in poorly lighted houses, become slen- 
der, producing elongated petioles and stunted leaves 
with little green color in them. Such plants, too, 
are soft, and possess little of the solid or resistant 
tissue. Poor light also makes cucumbers, as well 
as most other hothouse plants, susceptible to mil- 
dew, blight and leaf spots. Poor light and wet soils 
are responsible for the burning of the foliage of 
hothouse plants under fumigation. Too much light 
often affects the transpiration of plants and causes 
them to wilt unduly. Blossom end rot of toma- 
toes under glass is more severe under bright light 
than under partial shading. No fixed rules can be 
given as to the light requirements of greenhouse 
crops. Until more definite knowledge is obtained 
on this important subject, the greenhouse manager 
will of course depend on his common sense, observa- 
tions and experience to guide him. 



56 Diseases of Greenhouse Crops 



Construction and Management of Hothouses 
AS Affected by Light Conditions 

From the previous discussion, it is now evident 
that to improve light conditions indoors will tend to 
produce normal growth and to hasten maturity. 
The greater the photosynthesis, the more rapid the 
assimilation of plant food, hence the quicker the 
growth. An increased amount of heat can never 
replace the normal effect of an increase of light for 
those crops which most require it. Many growers,- 
especially those who possess poorly constructed 
houses, often attempt to substitute heat for light 
in forcing. The result is generally a failure, because 
diseases of all sorts find the tender weak plants an 
easy prey to their attacks. The modem greenhouse 
man is partly solving the light problem by con- 
structing larger houses and using larger glass. As 
a result of this, more air space and more uniform 
moisture distribution is assured. The double-thick, 
third quality glass, used in previous years, is now 
being replaced by a good grade of double-thick, sec- 
ond quality glass. Improvements are also being 
introduced in the roof angles, for these, too, mean 
added and better light. The more closely the angle 
of the roof coincides with the right angle cast by 
the sun's rays, the greater the amount of light that 
may reach the indoor plants. In the old form of 
houses, many of which are still in existence, the 
glass used was from two to seven inches long and 
two to five inches wide, and was often lapped more 



Light in Greenhouse Culture 57 



than an inch. This system practically excluded fifty 
per cent, of the light. The modern house uses glass 
varying in dimensions from 16 inches by 24 inches, 
20 inches by 30 inches to 24 inches by 24 inches. 
With the use of the larger glass, the diminished 
lapping results in a considerable saving of light. 
To prevent breakage of the larger glass a house must, 
of course, be solidly built and well purlined. 

The location of the house, too, influences the 
amount of light taken in. Houses located north and 
south are benefited by the morning light only, 
whereas those running west receive only the after- 
noon light. The ideal location from the light view- 
point would be to set the house on a line running 
20 to 25 degrees north of east. 

Houses with greater roof angles naturally receive 
more light. It is also a well conceded fact that 
light will pass through a transparent object more 
easily if it is placed at right angles to the light 
rays. This fact is not often taken advantage of 
by greenhouse builders. However, it cannot be de- 
nied that the sunlight strikes the house at differ- 
ent angles during the day and likewise at differ- 
ent seasons of the year, thus producing considerable 
variation in the amount of light reflected. To obvi- 
ate this, houses should be built with greater roof 
angles, a plan which will insure less reflection and 
thus allow a greater amount of light to penetrate. 
During Januar}', for instance, when the normal sun- 
light is naturally less, glass placed at an angle of 



58 Diseases of Greenhouse Crops 



60 degrees will absorb far more light than if placed 
at angles of 10 or 30 degrees. 

It has been the general belief that the light in 
the hothouse was greatest nearest to the glass. Ex- 
perience has disproved this. Modem houses are 
built larger, which means a greater distance between 
glass and plants. 

Effects of Various Colored Lights 

That plants require light for their normal de- 
velopment and for the proper performance of their 
function no one doubts. Crops grown outdoors 
naturally receive their light from the sun's rays. 
Plants within the gfeenhouse do not always receive 
the rays of the sun in a normal way. As a result, 
the health of these plants may often be impaired, 
or the quality of the product greatly affected. The 
researches of Flammarion* on this subject are of 
particular interest to the greenhouse man. 

Temperature Influenced by the Color of 

THE Glass 

Flammarion has shown that temperature is af- 
fected by the color of the glass. Houses differen- 
tiated by the following sorts of colored glass were 
tried: blue, approaching closely to violet; red tra- 
versed by a little orange; green and ordinary white 
glass. These four houses were placed side by side 

•Flammarion, Caraille. Experiment Station Record 10: 103-X14, 

1898. 



Light in Greenhouse Culture 59 



and equal conditions of care and culture were ob- 
served in all of them, approaching natural condi- 
tions as nearly as possible. The temperatures in 
these houses are given in Table 7. 



Table 7 



Time of day 


White 


Red 


Green 


Blue 


7:30 A.M. 


Degrees 
32.0 


Degrees 
31.0 


Degrees 
30.7 


Degrees 
295 


8:30 A.M. 


40.0 


39.5 


370 


35.0 


10:30 A.M. 


49.0 


46.0 


41-5 


40.0 


12:30 P.M. 


42.0 


40.0 


39.0 


38.0 


2:30 P.M. 


41.0 


40.5 


40.3 


40.2 


4:30 P.M. 


30.0 


30.0 


30.0 


30.0 



It is evident that the ability of the glass to absorb 
the sun's rays determines the heat in the hothouses. 
All rays are able to pass through white glass, which 
explains why the highest temperatures were found 
in this house. The lowest temperatures were found 
in the blue house, blue having the greatest absorb- 
ing power. It is striking that the temperature was 
apparently the same in all the hothouses during 
the cloudy weather and when the sun's rays did not 
penetrate directly. 

Plant Growth Influenced by the Color of 
THE Glass 

Experiments on sensitive plants showed the fol- 
lowing results: Plants placed in a red house de- 



6o Diseases of Greenhouse Crops 



veloped a height fifteen times as great as that in the 
blue house, where practically no growth was made. 
The red light in this case acted as a fertilizer. 
Moreover, the sensitiveness of the plants grown in 
the red house had increased considerably. The 
slightest movement or breath was sufficient to cause 
the leaflets to close, or the pedicels to droop. The 
sensitiveness diminished under the white or green 
color, while under the blue glass the sensitiveness 
was almost lost. The plants in the red house were 
first to bloom. In the white house they increased 
in stockiness and in vigor, but did not seem to in- 
crease in height. The plants in the house with the 
red glass possessed foliage which was lighter than 
those grown in the white house, while under the 
blue glass the foliage was much darker. After three 
months the height of the plants in the different 
houses was as shown in Table 8. 



Table 8 



Date 


Red 


White 


Green 


Blue 


June 13 


Meter 
0.030 


Meter 
0.030 


Meter 
0.030 


Meter 
0.030 


July 22 


0.230 


0. 120 


0.080 


0.035 


August 16 


0.380 


0.240 


0. 100 


0.035 


August 30 


0.470 


0.270 


0. 100 


0.035 


October 12 


0.500 


0.380 


0.100 


0.035 



From the preceding table it is seen that the 
plants in the hothouse with the red glass attained 



Light in Greenhouse Culture 6i 



greater height and exhibited more sensitiveness than 
those in the white house. The sensitive plants in 
the green hothouse made a little headway at first 
and then came to a standstill. In the hothouse 
with the blue glass practically no headway was 
made. In comparing the weight of the plants in the 
various hothouses with that of the height as previ- 
ously mentioned, the results will be found to be 
different. This is clearly seen in Table 9. 



Table 9 



Hothouse 


Weight of 
Stems and 
Leaves 


Weight of 
Average 
Leaf 


Diameter 
of 
Stem 


White 


Grams 
8.400 


Grams 
0.600 


Mm. 
30 


Red 


4.600 


0.250 


2.0 




0.300 


0.150 


1.5 


Blue 


0.150 


0.095 


1.0 





It is very curious to find that the plants in the 
red hothouse, although the highest, were not the 
heaviest. The weight was almost double in the 
white hothouse, although in height the plants did 
not compare to those in the red hothouse. 

Experiments on lettuce, similar to those on the 
sensitive plants, yielded like results. Lettuce grown 
in the white hothouse produced large thick . leaves 
with well rounded heads, in fact the plants here 
did not differ from those grown in the open. Let- 
tuce grown in the red house was drawn, its leaves 



62 Diseases of Greenhouse Crops 



long, straight, blanched and drooping. Those 
grown in the hothouse with green glass made a slight 
growth, but the leaves were more curled than those 
in the red house. In the blue hothouse, the lettuce 
plants added only a few leaves, without increasing 
the height attained in the first two weeks (fig. 9, 
i-j.). 

Experiments on peas and beans yielded similar 
results. In both plants the normal and most vigor- 
ous growth was found to occur in the white hot- 
house. The plants in the red hothouse were taller 
but thinner, while in the blue hothouse the minimum 
of growth occurred. The beans bloomed and fruited 
equally well in the white and in the red hothouses. 
In the green and in the blue houses the plants soon 
died. With the peas, blooming and fruiting seemed 
to be normal both in the white and in the red hot- 
houses. In the house with the green glass, the peas 
remained in bloom for three weeks, but did not 
fruit. In the blue house, the peas failed to bloom 
altogether. 

Experiments with ornamental plants, such as 
Coleus, yielded similar results. The Coleus in the 
white hothouse produced a normal well developed 
plant. In the red house there was an increase in 
height with a decrease in foliage. In the green 
and blue hothouses there was very little develop- 
ment (fig. 9, a-h.). 




BLUE G RFFN RED ' WHITE 



i j k I 



Fig. 9. AcTiox of Different Light Rays 

ON COLEUS AND ON LeTTUCE, 

a. Full radiation, h. red rays, c. green rays, 
d. blue rays, e. open air, f. subdued light, g. 
diffused light, h. very dim light, t. _ blue light, /. 
green light, k. red light, /. white light (a-/ after 
Flammarion). 



Light in Greenhouse Culture 63 



Root Development Influenced by the Color of the 

Glass 

It has already been seen that different rays of the 
solar spectrum may modify the parts of the plant 
above ground. The same effects may also appear in 
the root system of such plants. The root system is 
considerably smaller in the red hothouse than it is in 
the white hothouse. In the hothouse with green 
glass, the root system is very poorly developed, 
while in the blue there is almost no root system. 

Anatomy of the Plant as Influenced by Dif- 
ferent Rays of Light 

As we have seen, different rays of light are capa- 
ble of influencing the growth of plants. The same 
is also true of the structure of plants. Flammarion 
has found that sensitive plants, for instance, when 
grown in a white hothouse, possess a thicker epider- 
mis, more numerous wood fibers in the stem, and 
the pith was much less developed than was the case 
with similar plants grown in red, green or blue hot- 
houses. 

Effect of White and Colored Light on TranS' 
piration 

The effect of various lights on transpiration is 
shown in Table 10. 



64 Diseases of Greenhouse Crops 



Table lo 



Color 


Weight 

of 
Leaf 


Weight of 
Transpired 
Water 


Water Trans- 
pired per 
Gram of Leaf 




Grams 


Grams 


Grams 


Red 


0.135 


0.208 


1.540 


Yellow 


0. 102 


0.230 


2.254 


Green with some yel- 
low rays 


0.095 


0.065 


0.682 


Violet 


0.080 


0.024 


0.302 



It is thus seen that the greatest transpiration takes 
place under the yellow light, and the least under 
the violet. 



Effect of Various Light Rays on the Color of 

Plants 

It is well known that the green color of leaves 
which is due to chlorophyll can only be produced 
in the light. Other plant colors such as red, yellow, 
blue, may be due to the presence of colored pig- 
ments, or to color in the cell sap itself. 

That light and not temperature is capable of 
changing the colors in plants has been proven by the 
investigations of Flammarion. He found that lilac 
blossoms in a white hothouse became pink, and in 
red, green and blue hothouses the blossoms became 
white. If the lilac blossoms already colored are 
placed under a dark bell jar, they will turn from 
pale blue to clear red violet. This change of color 




i h 



Fig. 10. Action of Different Light Rays 
ON THE Color of Plants. 

a. Red flowered Crassula in sunlight, b. same in darkness, c. Alter- 
nanthera amoeua full radiation, d. same under red rays, e. geranium 
leaves full radiation, f. same under blue rays, g. green rays, h. red rays 
{a-h, after Flammarion). 



Light in Greenhouse Culture 65 



is not due to temperature. It is due solely to the 
effect of various light rays. Lilac blossoms, for in- 
stance, if enclosed in a dark chamber will become 
discolored, irrespective of surrounding temperatures. 

Coleus plants grown in a white hothouse will 
produce leaves with the normal amount of red color 
and pigm.entation. In a red hothouse, the red pig- 
ment of the Coleus decreases, the leaves are more 
spread, and their form is changed. Coleus grown 
under green-colored glass produces leaves of small 
sizes, the pigments almost disappear, and give place 
to a yellow coloration. The same is true also when 
Coleus is grown under blue glass. In this case, 
however, the red pigments disappear almost com- 
pletely (fig. 9, a-d.). In substantiation of the 
fact that light is capable of transforming plants, 
Flammarion refers us to the following experiment: 
Coleus plants may gradually be transformed when 
grown under a slightly diffused light through a gar- 
den frame, in diffused light, and in still weaker 
light. The plants grown in the open are of course 
normal. The most curious transformation occurs 
in the diffused light. Here the leaves enlarge con- 
siderably and the red pigments diminish in the cen- 
ter. Under a weak light the Coleus leaves become 
stunted, and the color changes from poppy red with 
a dark edge to yellow with a light green edge (fig. 
9, e-h.). Purple leaves of Alternanthera amena will 
become green under red glass. In the open, gera- 
nium leaves possess a reddish brown tone. This color 
changes under red, green or blue rays (fig. 10, a-h.). 



66 Diseases of Greenhouse Crops 



These experiments seem to indicate that light is of 
itself able to modify plants. 

Effect of Light on Disease Resistance 

It has already been seen that light is an important 
factor in plant culture. It alone seems able to 
change the form of a plant as well as its color. 
Moreover, the resistance of a plant to a disease may 
be modiiied by light. Damping off, for instance, 
a prevalent disease in greenhouses, is more virulent 
on dark cloudy days, when the light in the hothouse 
is abnormal and weak. A temporar}* change in the 
normal functions of the metabolism of the plant 
occurs and is followed by a sudden lowering of 
vitalit}% The greenhouse man cannot overlook the 
importance of the light requirement of plants under 
glass. Experience has shown that white glass is 
the only one capable of furnishing the necessary 
light rays to the plant. Needless to say, that only 
the best quality should be secured, for economies in 
the qualit}^ of glass may not always be the wisest nor 
the cheapest in the end. 

Electro-Culture 

The field of greenhouse culture is a plastic one. 
Electricity is undoubtedly capable of influencing 
plant growth. The greenhouse man who is conscious 
of the possibilities of control in his plastic domain 
will not neglect this phase of plant culture. 



I 

Light in Greenhouse Culture 67 

Effect of Electric Light 

It has always been a question whether growth 
under hothouse conditions could not be hastened by- 
using artificial light at night. The work of Rane"^ 
has shown that such is the case. 

The beneficial effect on lettuce seems to be espe- 
cially marked for the Grand Rapids variety first, 
next for the Hanson and thirdly for the Tennis 
Ball, the only three varieties experimented on by 
Rane. The lettuce in the house lighted with elec- 
tricity seemed more erect, vigorous, and the soil 
freer from damping off and rot-producing organ- 
isms. This is indeed an important consideration. 
Moreover, the lettuce in the electrically lighted 
house matured about twelve days earlier than that 
grown otherwise. Greenhouse spinach, like lettuce, 
seems also to be benefited by electric light at night. 
On the other hand, cauliflower reacts poorly to this 
treatment. Although the plants are taller, the qual- 
ity of the head is of an inferior grade. Radishes 
develop more tops than roots. The practical- 
minded greenhouse man will use electric light at 
night to induce extra stimulation for those green- 
house crops that respond favorably to it. The cost 
of installing the system certainly cannot be consid- 
ered as a real drawback. Electricity in these days 
may be obtained at a reasonable price. This is es- 
pecially true of greenhouses situated near large 

*Rane, F. W., West Virginia Agr. Expt Sta. Bui. 37, Vol. 4, 
No. i: 3-27, 1894. 



68 Diseases of Greenhouse Crops 



cities. But more extensive investigations are needed 
to convince the grower of the practicability of the 
attempt. 

Effect of Shading 

It has been shown in the previous chapter that 
certain light rays, such as green or blue, are detri- 
mental to plant growth. On the other hand, the 
normal sun rays from outdoors or as they come 
through white glass are most conducive to normal 
plant culture. The practical man, however, real- 
izes that at certain times of the year, especially dur- 
ing the summer months, the white glass must be 
shaded to prevent an excess of sunlight. This is 
accomplished by whitewashing the glass. That this 
procedure is necessary no one can question. How- 
ever, it must be admitted that the method itself is 
still a crude one, inasmuch as the various plants 
in the hothouse are subjected alike to the same 
amount of shading. Shantz* has shown that while 
a certain amount of shading is beneficial to plant 
growth, yet not all plants are benefited alike by 
this treatment. 

Effect of Different Light Intensities on 
Plants 

The work of Shantz distinctly shows that all 
plants do not tolerate the same amount of shading. 
To prove this he grew various crops in a bed cov- 

♦ Shantz, H. LeRoy, U. S. DepL Agr. Bur. PI. Ind. Bui. 279: 7-29, 
1913. 



Light in Greenhouse Culture 69 



ered with cloths of different textures. The arrange- 
ment of the cloth and the amount of light penetrat- 
ing it are shown in Table 1 1 . 



Table 11 

Method of Determining the Effect of Different 
Light Intensities 





I 


2 


3 


4 




6 


Cloth Used 


Black 
Duck 


Light 
Canvas 

Cloth 
{Black) 


Cham- 
bray 


Light 
Cham- 
bray 


Voile 


No 
Cover 


Fraction of normal light 
■capable of passing 


1/93 

or 
n/93 


1/15 
or 
n/iS 


1/7 
or 
n/7 


1/5 
or 

iign/s 


1/2 
or 
|n/a 


I 

or 
n 



As an explanation to Table 11, in referring for 
instance to column marked 2, n/ 1 5, we mean the 
second section of the bed where light canvas cloth 
(black) was used for shading, and where the light 
capable of passing through was equivalent to 1/15 
or ^/i5, I ox n represents the normal. The same 
interpretation is given to the other sections of Table 
11, all of which really correspond to the sections of 
the bed experimented with, it being remembered 
that I ox n represents normal light. 

Effect of Different Light Intensities on 
Lettuce 

According to Shantz, lettuce could not grow in 
section 1 under ^2/93 illumination, as the seedlings 
died as soon as the reserve food material in the 
cotyledons was consumed. In section 2, n/\$ 



70 Diseases of Greenhouse Crops 



illumination, growth was barely possible. The 
plants in this case were emaciated and worthless. 
It seems, therefore, evident that lettuce cannot stand 
shading where the light is reduced to ^2/15. The 
greatest amount of gain is made by lettuce when 
the intensity of the light ranges between n/^ and 
n/^. At this point the stimulation is greater than 
in those grown under normal light or even at n/l.. 
In full light lettuce plants are smaller than in /z/y 
or n/ ^ light. In flavor, a very slight change only 
may be noticed between plants grown under full 
light and those receiving n/l. light. However, un- 
der n/ ^ illumination the strong taste seems to dis- 
appear entirely. When the light is reduced to n/'^ 
the flavor seems to improve even more. Moreover, 
in this case the plants acquire the particular form of 
growth required by the market more consistently 
than do those that are produced in brighter light. 

Effect of Different Light Intensities on 
Radish 

Young radish seedlings seem capable of standing 
about 30 days under ^2/93 illumination. At the end 
of that time, however, they die. In z?/ 1 5 light there 
is almost no growth. The best gains seem to be 
made under a light of n/l. or n/ ^, In this respect, 
the shade tolerance of the radish is somewhat simi- 
lar to lettuce. However, the effect of shade is not 
noticeable in the flavor of the radish. 

From the above evidence it is apparent that plant 
growth is assisted by shading, the degree of which 



Light in Greenhouse Culture 71 

must be worked out for each specific crop. Ordi- 
narily, under greenhouse conditions, shading is ac- 
complished by means of whitewashing the glass of 
the hothouse. It would seem more desirable to use 
chambray, light chambray or voile cloth instead of 
whitewashing. The cloth could be installed on a 
system of rollers, so that when shading is necessary 
it could be spread out on the glass and when not 
needed it could be rolled up again. This would 
enable the greenhouse man to retain the full amount 
of normal light on cloudy days, an advantage which 
cannot be obtained when the glass is whitewashed. 
The substitution of cloth for whitewashing offers 
a good field of experimentation, both for the labora- 
tory and for the practical man. 

Heat Requirement 

The heat requirement of indoor crops demands 
the closest attention and study. As is well known, 
no two crops require the same temperature for their 
maximum development and production. Moreover, 
the same plant requires different temperatures in 
its various stages of growth. To appreciate thor- 
oughly the relationship of heat to plant life, we 
may liken the plant to a steam engine. With very 
slight steam pressure, the engine remains "dead," 
because it is not able to overcome the friction of 
its own parts and hence is capable of no work. 
With the proper amount of steam pressure, the 
engine is capable of a maximum amount of work. 



72 Diseases of Greenhouse Crops 



However, if an excess of steam pressure is used, 
the engine under an excessive strain will break or 
explode. The same is true with plants. A low 
temperature may not suffice to awaken the active 
life processes. With increased temperature, the 
plant becomes capable of maximum activity. Tem- 
perature beyond the normal requirements causes it 
to suffer or even to die from weakness and disease. 

The ideal development with forced plants is pos- 
sible only if we consider the relationship of the soil 
temperature to that of the air. For instance, the 
bum of lettuce is brought about by rapid evapora- 
tion of moisture from the leaves at a time when 
the roots are unable to supply this excessive demand 
of water. If the soil is cold, or its temperature dif- 
ferent from that of the house air, the roots will be 
unable to supply fast enough the water needed by the 
foliage. This will result in their collapse or burn- 
ing, and the ruin of the lettuce crop. The proper 
temperature requirement for each crop will be taken 
up when we consider further the cultural require- 
ments of each. 



CHAPTER 5 



MOISTURE AND WATER REQUIREMENTS 

Moisture here means the humidity present in the 
hothouse atmosphere. The importance of this sub- 
ject is as yet little appreciated by the practical man» 
The investigations of Blake* on the moisture re- 
quirements of roses point to the urgent need of 
similar experiments on other commercial hothouse 
crops. 

In the greenhouse, temperature and humidity rank 
with food in their importance to the plants. 

Effect of Humidity on Rose Foliage, Frequently 
when a greenhouse crop fails, the soil, the fertilizer 
or the water receives the burden of the blame. Lit- 
tle does it occur to us that the cause of the failure 
may be due to improper adjustment of humidity to 
temperature and watering. That each crop requires 
different humidity conditions is well conceded. The 
maidenhair fern, for instance, will not thrive in a 
house with a dry atmosphere, a condition which is 
ideal for other plants such as ornamental cacti. 
With roses a low humidity tends to reduce the size 
of the leaves, and the latter become ''hard" and 
lose their flexibility. Again, vigorous, dark green 
foliage indicates a proper degree of humidity. 

* Blake, M. A., New Jersey Agr. Expt. Sta. Bui. 277: 3-55, 1915. 

73 



74 Diseases of Greenhouse Crops 



Relation of Temperature and Humidity in 
THE Greenhouse 

The investigations of Blake show (Table 12) that 
the humidity decreases in direct proportion to an 
increase in temperature. The opposite occurs when 
the temperature is lowered. 



Table 12 
Humidity as Affected by Temperature 



Date, 
1914 


Outdoor- 
Weather 
Conditions 


Time 

of 
Day 


Ventila- 
tion 


Heat 


Temper- 
lUture in 
Housd 


Humidity 


Feb. II 


Fair 


11:00 A.M. 


Yes 


On 


70 


72 


Feb. II 


Fair 


10:30 A.M. 


Yes 


OS 


64 


90 


Feb. 12 


Fair 


1 :30 P.M. 


None 


On 


62 


72 


Feb. 12 


Fair 


4:00 P.M. 


None 


On 


64 


70 


Feb. 13 




11:30 A.M. 


None 


OfiE 


68 


80 


Feb. 13 




3:30 P.M. 


None 


On 


65 


75 


Feb. 14 


Fair 


2:1s P.M. 


None 


OflE 


71 


82 


Feb. 14 


Fair 


5:00 P.M. 


None 


On 


61 


69 


Feb. 16 


Fair 


2:00 P.M. 


Yes 


OflE 


65 


95 


Feb. 16 


Fair 


5:00 P.M. 


None 


On 


63 


79 


Feb. 17 




8:00 A.M. 


None 


On 


60 


89 


Feb. 17 




1:00 P.M. 


Yes 


OflE 


67 


95 


Feb. 18 


Snow and rain .... 


8:00 A.M. 


None 


OfiE 


67 


90 


Feb. 18 


Snow and rain. . . . 


3:45 P.M. 


None 


OflE 


64 


86 


Feb. 20 


Fair 


11:00 A.M. 


Yes 


OfiE 


67 


90 


Feb. 20 


Fair 


4:30 P.M. 


None 


On 


64 


85 


Feb. 21 


Fair 


8:00 A.M. 


None 


On 


71 


65 


Feb. 21 


Fair 


1:00 P.M. 


Yes 


OfE 


72 


! 78 



Moisture and Water Requirements 75 



From Table 12 it is evident that heat lowers the 
humidity. It is also to be noted that the decrease in 
humidity is rapid on bright days even when most 
cold. It is to be further noted that not only the 
heat, but the ventilation of the house during the 
day when the heat is turned on in the pipes, tends 
to reduce the humidity still further. Rose growers, 
for instance, are aware that at the approach of 
spring the plants suddenly improve greatly. This 
is generally attributed to longer and brighter days. 
However, according to Blake, this change is due to 
an increase in humidity in the hothouse due to the 
shutting off of the heat in the pipes. 

Effect of Humidity on Greenhouse Crops 

For further information on this subject, we have 
to refer again to the researches of Blake. He finds 
that the American Beauty rose, for instance, as a 
result of insufficient humidity fails to produce new 
shoots from the base of the plant. Moreover, the 
foliage, except at the tips of the growing shoots, be- 
comes hardened and toughened. The older leaves 
turn yellowish and fall off prematurely, leaving 
bare stalks. As a result of this the younger and 
smaller rootlets die out. Blake also found that a 
high humidity tends to increase the size of the foli- 
age, and the flowers seem to be likewise favorably 
affected. With low humidity the leaves of small 
rose plants wilt on bright days, even though the 
soil is kept moist. Frequently the leaves turn black, 



76 Diseases of Greenhouse Crops 



which is really a form of sunburn. This is un- 
doubtedly caused by the dryness of the atmosphere 
in which the moisture in the leaves is given off faster 
than the roots can supply it. 

Humidity as Affected by Walks in the House 

There seems to be a tendency among modem 
greenhouse men to build benches and sidewalks of 
cement. While this may be very desirable from a 
hygienic viewpoint, it is objectionable for the main- 
tenance of the proper degree of humidity. It is 
extremely difficult to raise the humidity of a house 
with cement walks. This is true even when water 
is applied to the walks and sprinkled on the plants. 
In houses devoted to roses and similar plants, where 
it is desirable to maintain a humidity of at least 75 
per cent., cement walks become quite objectionable; 
cinder walks are to be recommended instead. Ce- 
ment walks may be readily transformed by cover- 
ing them with a layer of six inches of cinders. This 
covering will make it possible to maintain a higher 
and more uniform humidity. 

Humidity is also an important factor in the heat- 
ing of glass houses. The greater the humidity the 
greater is the evaporation of moisture, and the 
greater is the amount of heat required to maintain 
a uniform temperature. Without proper attention 
to these conditions, the hothouse crop may be 
doomed to failure. 



(t 






II 




1 


1= 


J f 




1 

a 


1 i 


1 



Fig. II. 

a. Sling psychrometer, an instrument 
used to determine the relative humidity 
in the air, b. case cover. 



Moisture and Water Requirements 77 



Humidity Determination in the Greenhouse 

Perhaps the quickest and safest way of determin- 
ing the relative humidity of the air in the hothouse 
is by means of a sling psychrometer (fig. 11.). 
This instrument is very simple in design. It con- 
sists of a wet and dry bulb thermometer attached 
to a wooden or metal support. The handle arrange- 
ment permits the instrument to be whirled in the 
air while taking the reading. The wet bulb ther- 
mometer is covered with muslin and is thoroughly 
moistened by being plunged into a cup of water 
which should be of the same temperature as that of 
the air of the hothouse. 

Method of Determining Humidity 

After wetting the muslin of the wet bulb ther- 
mometer, the instrument is whirled steadily for a few 
seconds and the reading of the wet bulb thermome- 
ter noted. This whirling is repeated several times, 
until the reading of the wet bulb thermometer is 
constant. At this stage, the difference of tempera- 
ture between the wet and dry thermometers is re- 
corded. After this difference has been obtained, we 
turn to Table 13 to get the exact reading of the 
relative humidity of the hothouse air. To make 
this clear to the reader, let us take a specific exam- 
ple. Suppose that the reading of the wet bulb ther- 
mometer was 64 degrees, and that of the dry bulb 
thermometer 62 degrees. This, then, will give us 



78 Diseases of Greenhouse Crops 

a difference of two degrees between the wet and the 
dry bulb thermometer. Let us now refer to the 
table under the column Dry hulh tliermorneter de- 
grees^ where it is marked 62 degrees. Read across 
Table 13 under the column depression of -wet bulb 
thermometer in degrees until the column indicates a 
difference of two degrees. In this case it is the 
fourth column. The resultant figure, 89, will be 
the relative humidity of the hothouse air. In other 
words, a temperature of 62 degrees of the dry bulb 
thermometer with a difference of two degrees of the 
wet bulb thermometer will give a reading of 89 
relative humidity of the air. In like manner, and 
by referring to Table 13, which should be hung up 
at a convenient place in the hothouse, the relative 
humidity of the house may be obtained. There are 
other simpler instruments by means of which the 
reading of the relative humidity may be obtained 
directly without the use of tables. The Mithoff 
hygrometer, for instance, is a type of such an instru- 
ment. However, they may readily get out of com- 
mission, and thus become imreliable. 

Watering 

The importance of water for greenhouse plants 
cannot be too emphatically stated. It has been 
truly said that "he who does not know how to water 
plants does not know how to grow them." Water 
is essential to plant life. It has been intimated that 
some crops evaporate from the leaves an amount 



Moisture and Water Requirements 79 



Table 13 

Relative Humidity, Per Cent, — Fahrenheit Tem- 
peratures. Pressure ^o.o Inches 



Dry 
Bulb 
Ther- 



Depression of Wet Bulb 



mometer 
Degrees 


0.5 


1 .0 


1.5 




2.5 


3-0 


3.5 


4.0 


4-5 


SO 


5-5 


A 0 
0. 0 


A p- 
0.5 


7.0 




90 


93 


90 


o? 


8-3 

03 


oO 


77 


74 


71 


07 


04 


At 
01 


F<0 

So 


55 




97 


94 


90 


8t 
o? 




St 
ol 


tB 

7° 


75 


71 


AC 
OS 


Ar 
05 


Ao 
02 


59 


56 


52 


97 


94 


90 


87 


84 


81 


78 


75 


72 


69 


66 


63 


60 


57 




97 


94 


90 




04 


B T 

01 


tB 
70 


75 


72 


09 


AA 
00 


A-> 
03 


At 
01 


58 


54 


97 


94 


91 


88 


85 


82 


79 


76 


73 


70 


67 


64 


61 


59 




97 


94 


91 


QQ 

00 


05 


52 


79 


tA 
70 


73 


70 


AQ 

Oo 


Ap< 

65 


A^ 

02 


59 


fA 


97 


94 


91 


SQ 
00 




o2 


79 


70 


73 


71 


AQ 
OS 


Af 

65 


63 


60 


57 


97 


94 


91 


88 


85 


82 


80 


77 


74 


71 


69 


66 


63 


61 




97 


94 


91 




85 


83 


80 


77 


74 


72 


69 


66 


64 


61 


59 


97 


94 


91 


89 


86 


83 


80 


78 


75 


72 


70 


67 


65 


62 


60 


97 


94 


91 


09 


oO 


03 


B T 


7o 


75 


73 


70 


AC 

Oo 


Ar* 

OS 


A-» 

6? 




97 


94 


92 


59 


QA 
oO 


Q A 

84 


fir 
01 


70 


tA 

70 


73 


71 


AO 

Oo 


65 


63 


62 


97 


94 


92 


89 


86 


84 


81 


79 


76 


74 


71 


69 


66 






97 


95 


92 


09 


07 


Q A 

04 


02 


79 


77 


74 


71 


69 


67 


6l 
64 


64 


97 


95 


92 


90 


87 


84 


82 


79 


77 


74 


72 


70 


67 


65 


6S 


97 


95 


92 


90 


87 


8s 


82 


80 


77 


75 


72 


70 


68 


66 


66 


97 


95 


92 


90 


87 


8s 


82 


80 


78 


75 


73 


IT- 


68 


66 


67 


97 


95 


92 


90 


87 


85 


83 


80 


78 


75 


73 


IT- 


69 


66 


68 


97 


95 


92 


90 


88 


85 


83 


80 


78 


76 


74 


71 


69 


67 


69 


97 


95 


93 


90 


88 


85 


83 


81 


79 


76 


74 


72 


70 


67 


70 


98 


95 


93 


90 


88 


86 


83 


81 


79 


77 


74 


72 


70 


68 


71 


98 


95 


93 


90 


88 


86 


84 


81 


79 


77 


75 


72 


70 


68 


72 


98 


95 


93 


91 


88 


86 


84 


82 


79 


77 


75 


73 


71 


69 


73 


98 


95 


93 


91 


88 


86 


84 


82 


80 


78 


75 


73 


71 


69 


74 


98 


95 


93 


91 


89 


86 


84 


82 


80 


78 


76 


74 


71 


69 


75 


98 


96 


93 


91 


89 


86 


84 


82 


80 


78 


76 


74 


72 


70 


76 


98 


96 


93 


91 


89 


87 


84 


82 


80 


78 


76 


74 


72 


70 


77 


98 


96 


93 


91 


89 


87 


85 


83 


81 


79 


77 


74 


72 


71 


78 


98 


96 


93 


91 


89 


87 


85 


83 


81 


79 


77 


75 


73 


71 


79 


98 


96 


93 


91 


89 


87 


85 


83 


81 


79 


77 


75 


73 


71 


80 


98 


96 


94 


91 


89 


87 


85 


83 


81 


79 


77 


75 


74 


72 



8o Diseases of Greenhouse Crops 

Table 13 (continued) 

Relative Humidity^ Per Cent. — Fahrenheit Tern' 
peratures. Pressure ^0.0 Inches 



Thermometer in Degrees 



7-5 


8.0 


0 . 5 


9 • 0 


9-5 




10.5 




II . 5 




12 . 5 


13.0 


13.5 


14.0 


14. s 


15.0 


15.5 


52 


49 


40 


43 


41 


30 


35 


32 


29 


27 


24 


21 


tR 

lo 


rft 
10 


13 


10 


0 
0 


S3 


50 


47 


45 


42 


39 


ift 


34 


31 


28 


26 


23 




17 


15 




9 


54 


51 


49 


46 


43 


40 


37 


35 


32 


29 


27 


24 


22 


19 


17 


14 


II 


55 


52 


SO 


47 


44 


41 


39 


■2ft 
30 


33 


31 


oR 




23 


20 


tR 
10 


10 


13 


56 


53 


SO 


48 


45 


42 


40 


37 


35 


32 


29 


27 


24 


22 


20 


17 


IS 


57 


54 


51 


49 


40 


43 


41 


3° 


'}ft 
30 


33 


31 


oR 


20 


23 


21 


19 


10 


57 


55 


52 


50 


47 


44 


42 


39 


37 


34 


32 


30 


27 


25 


22 


20 


lo 


58 


55 


53 


50 


48 


45 


43 


40 


38 


35 


33 


31 


28 


26 


24 


22 


19 


59 


eft 


54 


51 


49 


/ift 
40 


44 


41 


39 


37 


34 


32 


30 


27 


25 


23 


21 


59 


57 


55 


52 


49 


47 


45 


42 


40 


38 


35 


33 


31 


29 


26 


24 


22 


60 


5° 


55 


S3 


SO 


4° 


40 


43 


41 


39 


37 


34 


32 


30 


28 


oft 
20 


23 


61 


50 


eft 


54 


51 


49 


47 


44 


42 


40 


30 


35 


33 


31 


29 


27 


25 


61 


59 


57 


54 


52 


50 


47 


45 


43 


41 


39 


36 


34 


32 


30 


28 


26 


f\'y 


f\n 
00 


57 


55 


53 


50 


4° 


40 


44 


42 


40 


37 


35 


33 


31 


29 


27 


63 


60 


58 


56 


53 


51 


49 


47 


45 


43 


41 


38 


36 


34 


32 


30 


28 


63 


61 


59 


56 


54 


52 


50 


48 


46 


44 


41 


39 


37 


35 


33 


31 


29 


64 


61 


59 


57 


55 


53 


51 


48 


46 


44 


42 


40 


38 


36 


34 


32 


30 


64 


62 


60 


58 


56 


53 


SI 


49 


47 


45 


43 


41 


39 


37 


35 


33 


31 


65 


62 


60 


58 


56 


54 


52 


50 


48 


46 


44 


42 


40 


38 


36 


34 


32 


65 


63 


61 


59 


57 


55 


53 


51 


49 


47 


45 


43 


41 


39 


37 


35 


33 


66 


64 


61 


59 


57 


55 


53 


51 


49 


48 


46 


44 


42 


40 


38 


36 


34 


66 


64 


62 


60 


58 


56 


54 


52 


SO 


48 


46 


45 


43 


41 


39 


37 


35 


67 


65 


63 


61 


59 


57 


55 


53 


SI 


49 


47 


45 


43 


42 


40 


38 


36 


67 


65 


63 


61 


59 


57 


55 


53 


51 


SO 


48 


46 


44 


42 


40 


39 


37 


67 


65 


63 


61 


60 


58 


56 


54 


52 


50 


48 


47 


45 


43 


41 


39 


38 


68 


66 


64 


62 


60 


58 


56 


54 


53 


51 


49 


47 


45 


44 


42 


40 


39 


68 


66 


64 


62 


61 


59 


57 


55 


53 


51 


50 


48 


46 


44 


43 


41 


39 


69 


67 


65 


63 


61 


59 


57 


56 


54 


52 


SO 


48 


47 


45 


43 


42 


40 


69 


67 


65 


63 


62 


60 


58 


56 


54 


53 


SI 


49 


47 


46 


44 


43 


41 


69 


68 


66 


64 


62 


60 


58 


57 


55 


53 


SI 


SO 


48 


46 


45 


43 


42 


70 


68 


66 


64 


62 


61 


59 


57 


55 


54 


52 


50 


49 


47 


45 


44 


42 



Moisture and Water Requirements 8i 



Table 13 (continued) 

Relative Humidity, Per Cent. — Fahrenheit Tern- 
peratures. Pressure jo.o Inches 



Dry Bulb 
Thermometer 
Degrees 


Depression of Wet Bulb 




lO . 5 


17.0 


17 • 5 


18.0 


lo . 5 




19 ■ 5 




20. J 




5 

7 


3 
4 


2 


































9 


6 


4 


I 


















g 




3 
















12 


10 


8 


5 


3 


I 












14 




9 


7 


5 














16 


13 




9 


7 


4 












17 


15 


13 


10 


8 


6 


4 


2 








18 


16 


^^4 






g 


5 


3 








20 


18 


16 


13 


II 


9 


7 


5 


3 


I 




21 


19 


17 


15 


13 


II 


9 


■ 

7 


5 


3 








18 


16 


14 






g 


7 


5 




24 


22 


20 


18 


16 


14 


12 


10 


8 


6 




25 


23 




19 


17 


15 


13 






0 
0 




26 


24 


22 


20 


18 


17 


15 


13 


II 


9 




27 


25 


24 


22 


20 


18 


16 


\t 


12 


11 




29 


27 


25 


23 


21 


19 


17 




14 


12 




30 


28 


26 


24 


22 


20 


19 


17 


15 


13 




31 


29 


27 


25 


23 


21 


20 


18 


16 


IS 




32 


30 


28 


26 


24 


23 


21 


19 


18 


16 




33 


31 


29 


27 


25 


24 


22 


20 


19 


17 




33 


32 


30 


28 


27 


25 


23 


22 


20 


18 




34 


33 


31 


29 


28 


26 


24 


23 


21 


19 




35 


34 


32 


30 


29 


27 


25 


24 


22 


20 




36 


34 


33 


31 


29 


28 


26 


25 


23 


21 




37 


35 


34 


32 


30 


29 


27 


26 


24 


23 




38 


36 


34 


33 


31 


30 


28 


27 


25 


24 


r 


39 


37 


35 


34 


32 


31 


29 


28 


26 


25 


} 


39 


38 


36 


34 


33 


31 


30 


28 


27 


25 




40 


38 


37 


35 


34 


32 


31 


29 


28 


26 




41 


39 


38 


36 


35 


33 


32 


30 


29 


27 



60. 

61 
62. 

63. 
64. 



65. 

66, 
67. 
68. 
69. 



82 Diseases of Greenhouse Crops 

Table 13 (continued) 

Relative Humidity, Per Cent. — Fahrenheit Tern" 
peratures, Pressure jo.o Inches 



Thermometer in Degrees 





21 . 5 




22 . s 


23 . 0 


23 • s 


24.0 


24- S 


25 . 0 


25 ■ S 


26 0 


20. 5 


27 . 0 


27 . 5 


28 . 0 




X 


























'1 




- 


3 


I 






























4 


2 


I 




























0 


4 


2 


0 


























7 


6 


4 


2 


0 
























9 


7 


S 


4 


2 


0 






















10 


9 


7 


5 


3 


2 


0 




















12 


10 


8 


7 


S 


3 


2 




















13 


II 


10 


8 


6 


5 


3 


I 


















14 


13 


II 


9 


8 


6 


5 


3 


I 
















IS 


14 


l'2 


II 


9 


8 


6 


I 


3 


I 














17 


15 


U 


13 


10 


9 


7 




t 


3 


I 












18 


16 


IS 


13 


13 


10 


9 


7 




4 


3 


I 










19 


17 


16 


14 


13 


11 


10 


8 


7 


5 


4 


3 


I 








20 


18 


17 


IS 


14 


13 


II 


10 


8 


7 


S 


4 


3 


I 






21 


20 


x8 


17 


IS 


14 


12 


II 


9 


8 


7 


S 


4 


3 


X 




22 


21 


19 


18 


16 


IS 


13 


13 


II 


9 


8 


6 


S 


4 


3 


Z 


23 


22 


20 


19 


17 


16 


14 


13 


12 


10 


9 


8 


6 


5 


4 


3 


24 


23 


21 


20 


18 


17 


16 


14 


13 


II 


10 


9 


8 


6 


5 


. 4 


25 


23 


22 


21 


19 


18 


17 


IS 


14 


13 


II 


10 


9 


7 


6 


5 


26 


24 


23 


22 


20 


19 


18 


16 


IS 


14 


12 


II 


10 


9 


7 


0 



Moisture and Water Requirements 83 



of water equal to about three hundred times the 
weight of the dry matter which they contain. The 
amount of water in the soil is also an important con- 
sideration. The more water a soil contains the less 
air it will have. The presence of too much water 
in the soil often brings about serious complications 
in the health of plants such as suffocation of the 
roots, weak growth and a loss in power of resistance. 

The improper use of water may affect the physi- 
cal structure of the soil and injure the plants. The 
careless dashing of water on the surface of hothouse 
benches will compact and puddle the soil, and tend 
to wash down the smaller grains to the bottom, 
changing thereby the capacity of that soil to retain 
air or heat, and thus indirectly affect the health of 
the plants. 

Greenhouse plants depend on irrigation for their 
water entirely. Surface watering is still in use by 
the majority of hothouse men. But at best, this 
method often does no more than pack the soil in- 
stead of saturating it. Moreover, while safe enough 
for the experienced grower, it becomes extremely 
unsatisfactory when entrusted to careless or inex- 
perienced labor. 

SUBIRRIGATION 

It has been hinted previously that subirrigation 
has not found general favor with greenhouse men. 
Yet this has proved both experimentally and in 
practice to be far superior to any other form of 



84 Diseases of Greenhouse Crops 



greenhouse irrigation. In subirrigation water is ap- 
plied through tiles underground. 

Effect of Subirrigation on Vegetable Crops. In- 
vestigations by Rane* have clearly shown that pars- 
ley, tomatoes, long rooted radishes and spinach are 
greatly benefited by subirrigation. Lettuce, espe- 
cially, seems to be most favorably influenced by this 
method of watering (fig. 12, a-c). Little is known of 
the effect of subirrigation on flowering plants. In- 
vestigations along those lines are especially desirable. 

From the health viewpoint, subirrigation should 
appeal to greenhouse men. Where lettuce drop is 
prevalent subirrigation seems to check it materially. 
The same is also true of damping off. 

In the greenhouse, subirrigation may be adapted 
to any form of bed used, whether raised or solid. 
In either case the bed should be practically water- 
tight. To prevent the rotting of wooden beds Taft t 
, recommends coating the inside of the beds with a 
cement made of one part of water lime and three 
of sharp sand. This is made into a thick paste and 
spread over the surface about one-fourth of an inch 
thick. For a bed with tile or slate bottoms a simi- 
lar covering will render them sufficiently tight. 
With wooden benches it is desirable that the sup- 
ports be close enough to prevent sagging of the 
beds. In case of solid beds, a tight bottom about 
eight inches below the intended level of the bed is. 

*Rane, F. W., West Virginia Agr. Expt. Sta. Bui. 33: 255-270, 
1893. 

tTaft, L. R., Year Book, U. S. Dept. of Agr.: 233-246, 1895. 




sm- 

LRJUGATION 



ORDINARY 




SUB- 

mnroATioM 



O-RdJMAW 



5UB- 

mniGATFon 



OPDIMARY 




Fig. 12. Effect of Subikrigation on 
Lettuce. 

a. Boston curled, b. Frankford head (a-c after 
Rane, F. W.). 



Moisture and Water Requirements 85 



necessary. If the subsoil is a stiff clay it may be de- 
sirable to spread an inch of gravel. After thor- 
oughly ramming it is covered with a thin layer of 
the cement as described above. 

Overhead Irrigation 

This method is in greater use than any other prac- 
tice of greenhouse watering. The advantages claimed 
for it are the cheapness of installation and the more 
uniform way in which the water is applied. By this 
method, too, the dry atmosphere of the house can be 
quickly changed. This is especially desirable during 
the hot summer days. The disadvantages of this 
system are the packing of the surface soil and the en- 
couragement of disease through the excessive mois- 
ture applied to the plant. 

Ventilation 

Next to watering, ventilation is of utmost im- 
portance from the health viewpoint. Many of the 
plant diseases which are confined to the greenhouse 
are encouraged by improper ventilation. The lack 
of it is as harmful as an excess. The practical grower 
will give this careful thought and consideration. 
As a rule, plenty of ventilation should be given 
whenever weather conditions permit it, avoiding, 
however, draft and strong air currents. 



C TA^PTER 6 



BREAKING THE REST PERIOD OF PLANTS 

The object of greenhouse culture is to grow cer- 
tain crops or blooms at a time and season when 
these cannot be produced outdoors. All plants un- 
dergo a period of rest. Bulbs, for instance, enter 
their resting state when the leaves all die. No mat- 
ter how cold, warm or wet, bulbs will not grow 
again before the fall. Howard^ has found that it is 
very difficult to shorten this dormant period, at least 
during the earlier phases of the rest. He further 
found that of all treatments, drying, followed by 
injection with ether and Knop's solution (made up 
as follows: Calcium nitrate i gr., magnesium sul- 
phate 25 gr., acid potassium phosphate 25 gr., and 
water 1 liter.), and combinations of these were most 
effective in shortening the rest period of bulbs. The 
injection may be accomplished by piercing the bulb 
with a hypodermic needle. Herbaceous perennials, 
too, like the bulbs, undergo a rest period. Frost, 
drying, and ether appear to be the most effective 
agents in breaking this rest period. To treat plants 
with ether, a galvanized iron chamber is preferred. 
The latter as used by Howard is shaped like a cylin- 

* Howard, W. L,, Missouri Agr. Expt. Sta., Research Bui. 15: 
3-25, 1915. 

86 




Fig. 13. Effect of Etherization on Plants. 

b. Baptisa australis, 24 hours; c. check; a. 12 hours, f. Stokesia cyanea, 
check, d. etherized 24 hours; e. etherized 12 hours (a-f after Howard, W. L.). 



Breaking Rest Period of Plants 87 



der, with a diameter of about two feet and is made 
in two sections, each about three feet in length. The 
lower section is fitted with a bottom and at the top, 
around the rim, with a groove which is filled with 
fine sand. The rim of the upper section flares out^ 
so as to accommodate a lid. The latter fits in tightly 
by being forced down in the sand. The second sec- 
tion of the cylinder is like the first, except that it 
is bottomless. When treating a large number of 
plants at one time, the second section is placed upon 
the first, the lower end being forced into the sand. 
The ether is poured in through an opening in the 
lid, which may be tightly closed by means of a 
screw cap. The amount of ether used is at the 
rate of 40 grams to each 100 meters of space. The 
lid is weighted with bricks to prevent its being 
pushed off by the ether vapor. Treatments should 
preferably be given in the afternoon, or where there 
is no likelihood of changes of temperatures. The 
results of the treatment are summarized by Howard 
in Table 14 on following page. 

From Table 14, it is seen that with certain plants 
etherization breaks the rest period and hastens 
growth (fig. 13, a-f.) while with others the treatment 
has the opposite effect. In his investigations How- 
ard* further found that the rest period of a large 
number of woody plants may be largely overcome by 
ether treatment (fig. 14, a-b.). On the whole, how- 

♦Howard, W. L., Missouri Agr. Expt. Sta., Research Bui. i6: 
3-27, 1915. 



88 Diseases of Greenhouse Crops 



Etherized 
48 Hours 




Growth 
Began 

in 
Days 




Etherized 
24 Hours 


Fully 
Open 

in 
Days 


^ ++ ++■«• ++ ++ * +♦++ ■M"Si+ 


Growth 
Began 

in 
Days 


« -(-vO 11 4-Oi||iJ^»Oi/^Oi OOOiO linrOl 
M M ++ 1 1 jtO N C* w w Ci >/» 
^ ++ * ++++++ » 


Etherized 
12 Hours 


Fully 
Open 

in 
Days 


+- N 1 1 1 1 I '^-J- II "♦-llll ll-H-l 

« 1 « i 1 M o> M ! 1 1 1 ;5 M 1 1 i 


Growth 
Began 

in 
Days 




Etherized 
5 Hours 


Fully 
Open 

in 
Days 


w III w|o rON rjrro 

M ++ 1-1 ++ +4, t 1 1 ► 

++ +4- 


Growth 
Began 

in 
Days 


1 i 1 +-« M 1 OvO 1 1 -i-OO-i— rO 1 -t-OO l/» -f- I +- ! 
* -t-H-fr * M ' 4_» 4-^ ' 4^.+4. 
++ 


Dried 
8 Days 


Fully 
Open 

in 
Days 


+~ 4— t-Os-*- +-eO rflfl Oi N ■»-Tf4- 1 M 4-NM 4-1^4-0 
M M in <N 10 Ov ir> ro <N 1 ro ic fO vo fO 
tH ■< 1 1 »l 1* t 1 1 1 1 » 4-f 4-» 4-H-* ++ ++ 
♦ 


Growth 
Began, 

in 
Days 


4— +-00Oi« 4— ir><S <N\Ot^00 4- CS 4— 1 irt 4— vO w 4— CS4— O 
W fO +4- Tl- (N Irt (M Ci 1 M «N Tt N 
^*Ht¥ ♦HI* M' 1 < t » 4-I- 4-* 4-*4-» 4-fr 4-+ 


Frozen 
24 Hours 


Fully 
Open 

in 
Days 


U> 4-4- 1 rl" 4->0 1 4-4-4-»0 O N|4-JI0 4-UJ0 fC4- f. 
4-> ++ 4-»- +++♦ ** ** ♦*+-»• 4->4-> 4-» 


Growth 
Began 

in 
Days 


00 00 0 1 \0 00014— 04— MOv 00 1 4—100 4— tOO\ ^- rf'-t— 00 
4-t' 4-»M Tt w+4. M 0++ w w 4-M-» 4-t- w M 
4-t. 4-|.4-> -M>+* ++ ♦+ > 4-l-4-» 


i 


Fully 
Open 
in 
j Days 


4— 4— M rf Tt 4-4—4—0(^4—4—0 4— 00 m M t 1 H 4—04—01 
vO W »^ N Tt W 0 fO fO <M 
4->4-++4' -M-* 4-f ++^-M"M- ++ ++ 


Growth 
Began 

in 
Days 


4— 4— »*fOO 4— 4— N W54— r» »0 4— lOrorfTt 4— 't4— 4- «4— O 
M4-ffO IflMM t^fO N M C» N to fO « 



: > : 



• • +3 »-• 

: : 3 : 

2 • J? -22 



<jj as 



« S.2 =J S fl 



UUQQQWOM 



, >-< V> (J -rg 

•S-^gc >>• 
<u o 



■> • d-a 2 



; • ■ n? to _ C3 

' ^ m -t^-S O'S r-l 
I >H ^ r; Tj 



Breaking Rest Period of Plants 89 

ever, the use of anaesthetics is still in the experi- 
mental stage, although much that has been already 
discovered could be applied with great advantage 
commercially. 



PART III 

DISEASES OF GREENHOUSE VEGETABLES 



CHAPTER 7 



NATURE OF PLANT DISEASES 

The successful greenhouse operator will realize 
the necessity of recognizing readily any plant dis- 
ease. Very often this is overlooked and attention is 
attracted only when the trouble takes the form of an 
epidemic, and a large number of plants are thus 
carried off by it. 

Plant diseases are usually of four kinds : 

1. Those of a mechanical nature. 

2. Those brought about by physiological dis- 
turbances or unfavorable environment. 

3. Those brought about by parasitic flowering 
plants, fungi or bacteria. 

4. Diseases the cause of which is unknown. 

A familiarity with the symptoms of diseases will 
enable us to determine the contagious nature of the 
trouble and often the methods of control to pursue. 
The following outline* briefly summarizes the prin- 
cipal symptoms of disease in plants : 
1. Discoloration or change of color, 
a. Pallor, yellowish or white instead of the nor- 
mal green. 

♦Adapted with slight modifications from Heald, F. D., Texas 
University Bui. 135, Sc. ser. No. 14: 7-8, 1909. 

93 



94 Diseases of Greenhouse Crops 



b. Colored areas or spots. 

White or gray^ such as mildews, white 

rusts, etc. 
Yellow^ many leaf spots. 
Ked or orange^ rusts, leaf spots. 
Brown, many leaf spots. 
Black, black rusts. 
Variegated, leaf spots, mosaic 

2. Shot hole, perforation of leaves. 

3. Wilting, wilts, damping off. 

4. Necrosis, death of parts such as leaves, twigs, 
stems, etc. 

5. Atrophy, dwarfing or reduction in size. 

6. Malformations or excrescences, galls, pus- 
tules, tumors, cankers, rosettes. 

7. Exudation, slime or gum flow. 

8. Rotting, dry or soft rots. 

1. Diseases of a Mechanical Nature 

Greenhouse plants, contrary to those grown out- 
doors, are open to but few injuries of a mechanical 
nature, for it is seldom, indeed, that indoor plants 
are injured by rain, hail, or frost. 

Sunburn. While most greenhouse crops require 
a great deal of light, a few are injured by it. Some 
varieties of tomatoes, the Earliana especially, under 
the influence of strong sunlight are subject to sun- 
scald. Sunburn may be overcome by shading the 
glass. Of the various shading materials, the cheap- 
est and quickest to use is air-slaked lime. The 



Nature of Plant Diseases 95 



most expedient to use is air-slaked lime which has 
been slaked dry by sprinkling lightly with water. 
This is diluted in water and applied as a spray. If 
new lime is used it will be more difficult to wash 
off later. Moreover, it seems that air-slaked lime 
sticks a good while, but rubs off easily. It is far 
more desirable to use shading material that must be 
applied twice in the summer than something that 
will stick hard and remain during the fall and win- 
ter season. 

Smoke injury. As a rule large greenhouse estab- 
lishments are situated near large cities which are 
centers of industrial production and manufacture. 
Greenhouse plants are often injured from the effect 
of smoke or gases which escape from the furnaces 
into the air. 

The sources of smoke may be classified into three 
divisions: (i) Smoke from large buildings or from 
manufacturing plants; (2) Smoke from locomo- 
tives; (3) Smoke from chimneys of dwelling houses. 
Smoke is generally produced because of improper 
furnace construction, such as improper draft, over- 
loaded boiler, insufficient air space, insufficient air 
supply to boiler room, and also by carelessness qf 
operation. 

Smoke contains large quantities of carbon dioxide, 
steam and sulphur dioxide, besides its characteristic 
soot. The latter consists of carbon, tar, and mineral 
matter mixed with small quantities of sulphur, 
arsenic and nitrogen compounds which are of an 
acid nature. Soot adheres to plants, especially to 



96 Diseases of Greenhouse Crops 



foliage, giving them a burned, contorted appearance. 
Another effect of soot and smoke is to close up the 
stomata or respiratory openings of the leaf, so that 
asphyxiation results. The effect of smoke on plants 
is a loss of leaflets in case of compound leaves, and 
an abnormal curling and distortion. Lesions and 
spots may be formed on the foliage as a result of the 
sulphur dioxide which is present in smoke. The 
spots are at first small, but soon enlarge and finally 
involve the whole leaf, which dries and becomes 
gray. Smoke injury, although of a mechanical na- 
ture, may also be considered from a physiological 
point of view. The after effect of smoke on plants 
resolves itself into a question of insufficient food 
supply and assimilation. This is indirectly brought 
about by diminished illumination, interference with 
the normal transpiration and the reduction of leaf 
surface. 

Methods of Control, There is as yet no definite 
method of control known, consequently all that can 
be done is to avoid the smoke belts. The greatest 
injury usually occurs in locations to the leaward of 
smoky districts and when the soil is wet. As far as 
possible, therefore, postpone irrigation during the 
windy days. 

2. Physiological Diseases 

In this class are included disturbances which are 
due to unfavorable conditions of nutrition. There 
are numerous diseases of plants which are brought 



Nature of Plant Diseases 



97 



about by lack of, or by an excess of, certain food 
elements in the soil. The effect is an interference 
with the proper life functions of plants. 

Malnutrition 

Symptoms. The symptoms of malnutrition are 
not always the same. They differ somewhat with 
the crop, the nature of the soil, and the fertilizer 
applied. In malnutrition the symptoms to be looked 
for are retarded growth, change of color in the foli- 
age and root injury. Affected plants remain 
dwarfed at a time when maximum growth is ex- 
pected. The color of the foliage turns a lighter 
green, especially in the spaces between the veins, 
which become yellowish green to brown. Roots of 
such plants are poorly developed, and secondary 
roots are often missing. 

Causes of Malnutrition. The work of Stone*, 
and Harter f and others seems to have established 
the fact that malnutrition cannot be attributed to 
the work of parasitic organisms. Stone cites in- 
stances where constant watering with liquid fertil- 
izers or manure would cause malnutrition in cucum- 
ber plants. The same is also induced when pig and 
cow manure are mixed, or when manure is worked 
into a soil already well fertilized otherwise. Harter 
records cases of malnutrition brought about by an 

♦Stone, G. E., Massachusetts Agr. Expt. Sta., Ann. Rept., 5-13: 
X910. 

t Harter, L. L., Virginia Truck Expt. Sta., Bui. i: 4-16, 1909 
(Norfolk, Va.). 



98 Diseases of Greenhouse Crops 



excess of acidity in the soil. In soils where plants 
suffer from malnutrition, from 3,500 to 6,000 
pounds of lime per acre area are often required to 
neutralize the excess of the soil acidity. This con- 
dition is apparently the result of intensive trucking 
and the heavy application of chemical fertilizers 
which leave the soil acid. Sulphate of ammonia, 
muriate and sulphate of potash and acid phosphate 
when used continuously will leave the soil in a very 
acid condition. On the other hand, nitrate of soda, 
carbonate of potash and Thomas phosphate tend 
to make the soil alkaline. 

Another important cause of malnutrition is the 
exhaustion of humus. This is a natural result where 
commercial fertilizers are used instead of some form 
of organic manure. 

Methods of Controlling Malnutrition, It is quite 
obvious from what has already been said, that the 
greenhouse grower is the loser if he uses his fertilizer 
injudiciously. Not only is malnutrition favored by 
such a course, but the yields, too, are considerably re- 
duced. With acid soils, liming to neutralize the soil 
acidity will help control malnutrition. 

Chlorosis 

This disease may be attributed to several causes. 
Greenhouse plants that receive too much shade will 
become yellowish, then whitish, and in time may 
lose all their green color and finally die. Chlorosis 
is often brought about when plants grow in soils 



Nature of Plant Diseases 



99 



that have become too alkaline. This is true for 
soils containing an excess of lime, wood ashes, or 
magnesia, and especially when nitrate of soda is used 
in excess. 

Control, Chlorosis when brought about by the 
lack of available iron in the soil may be remedied 
by the application of small quantities of iron sul- 
phate. If the disease is caused by the other factors 
previously mentioned, a cure may be effected by re- 
moving the cause. 

Blossom Drop 

This is another trouble which may be termed 
physiological and the cause of which cannot be at- 
tributed to the work of parasitic organisms. It is 
often noticed on tomatoes and various other plants. 
Various causes lead to it. Sudden drops of tempera- 
ture at blossoming will induce many plants to shed 
their blossoms. Blossom drop may also be brought 
about when too much nitrogen is applied to the soil 
in the form of manure, especially hen manure. To 
overcome this, the fertilizer in the soil must be bal- 
anced by the addition of 600 pounds of acid phos- 
phate and 1 50 pounds of muriate of potash per acre. 
Overacidity in the soil may also cause the shedding 
of blossoms. A sudden checking of the water sup- 
ply, or overwatering may have the same effect. 
Finally, improper pollination is often one of the 
main causes for the blossom drop of greenhouse 
plants. In the field, pollination is favored by both 



100 Diseases of Greenhouse Crops 



wind and insects. In the greenhouse, these two 
agencies are practically shut out. With forced cu- 
cumbers, the difficulty is often overcome by install- 
ing beehives in the house. Bees are very active 
under high temperature conditions, and perfect pol- 
lination is the result. The usual practice is to sup- 
ply a beehive to every 2oo feet of house. The 
hives should be placed on platforms several feet 
above the bed to protect the bees from becoming 
drenched during the watering or sprinkling of the 
beds. We should bear in mind that the hives must 
be taken out whenever the house is fumigated with 
potassium cyanide. Nicotine fumes do not seem 
to injure the bees, especially if the fumigation is 
carried on at night. Bees may be used to pollinate 
practically every crop grown in the forcing house. 
It seems, however, that bees refuse to work on to- 
matoes, perhaps because of a dislike for their nec- 
tar. In this case, then, it is necessary to pollinate 
by hand. The investigations of Fletcher and 
Gregg* and others have shown that the setting of a 
good crop of smooth heavy tomatoes depends largely 
on the proper distribution of pollen over the stigma. 
A lack of pollination will of course result in no crop. 
An uneven distribution of pollen will result in too 
large or irregular fruit. During the winter and on 
sunny days, it will pay to go over the plants and 
tap each blossom with the finger or with a stick on 
which is fastened a small glass rod or spoon. This 

* Fletcher, S. W., and Gregg, O. T., Michigan Agr. Expt. Sta., 
Special Bui. 39: 2-10, 1907. 



Nature of Plant Diseases loi 



will shake out the pollen and enough of it will be 
liberated by this operation to insure complete fertili- 
zation. A high temperature will favor the maturing 
and the bursting of the pollen sacs even during 
cloudy weather. It is, therefore, advisable to run 
up the temperature of the house as high as is ex- 
pedient on the days when the tapping of the blos- 
soms is done. This should always be done during 
the day and never at night. The pollen sacks (an- 
thers or male organs) do not burst freely until after 
the yellow petals have fully expanded and have 
begun to wither slightly. The pollen is discharged 
most freely in a hot dry atmosphere. 

3. Diseases Brought About by Parasitic 
Flowering Plants or Micro-organisms 

In this class of diseases may be mentioned those 
which are induced by parasitic flowering plants such 
as the dodder and the broom rape. These, however, 
as well as the diseases induced by bacteria and fungi, 
will be considered under their respective hosts. 

Carriers of Diseases. In the greenhouse, dis- 
ease producing organisms are often brought directly 
with infected soil or manure in the compost. Fusa- 
rium lycopersici Sacc, the cause of sleeping sickness 
of tomato, as well as large numbers of other para- 
sites, are brought in that way. 

Little as yet do we realize the importance of in- 
sects as carriers and disseminators of plant diseases, 
although we are becoming increasingly aware of 



102 Diseases of Greenhouse Crops 



their role in human and animal pathology. Acting 
as carriers of spores of parasitic fungi, which may 
adhere to any part of their body, they are responsible 
for distributing plant diseases. Insects, too, by feed- 
ing on plants or in searching for the nectar of the 
blossoms, are likely to come in contact with diseased 
parts. Their bodies may become coated with spores 
of parasitic bacteria or fungi, which are thus car- 
ried from plant to plant and from field to field. 
The striped cucumber beetle is known to carry the 
virus of cucumber mosaic, and the germ of cucumber 
wilt {Bacillus tracheiphillus Ew. Sm.). It is there- 
fore very essential that every effort should be made 
to keep insect pests out of the greenhouse. 

4. Diseases of Unknown Origin 
Mosaic 

In this class will be included those diseases 
which spread by contact, but the exact cause 
of which is unknown. Special emphasis will be 
given to that important disease known as mosaicA 
This trouble attacks a variety of greenhouse plants. 
It is especially severe on the tomato, cucumber, and 
sweet pea. 

Symptoms. Mosaic is readily distinguishable by 
a yellow dotting or mottling on the foliage, present- 
ing in some instances a beautiful mosaic structure, 
whence its name. Affected leaves linger and often 
curl. 



Nature of Plant Diseases 103 



Cause of Mosaic, The cause of Mosaic is as yet 
a disputed question."^ Allard claims that mosaic is 
caused by an ultra-microscopic pathogen, that is, a 
parasitic organism which cannot be detected by our 
present technic in microscopy. Mosaic may be 
transmitted from plant to plant. The easiest way 
to prove this is to rub with the fingers a diseased 
leaf and then immediately rub a healthy one. The 
disease will appear on the inoculated host in about 
ten days. In the greenhouse, the green aphid and 
the white fly act as carriers of mosaic. 

Control. Methods of control in mosaic lie in the 
direction of prevention. Diseased plants should be 
destroyed by fire, and all indoor insect pests kept in 
check. 

* See also Taubenhaus, J. J., Truck Crop Diseases, E. P. Duttoa 
Co., 191 8, New York, N. Y. 



CHAPTER 8 



GERMINATION TROUBLES 

Diseased Seed, Numerous failures in germina- 
tion may be directly attributed to diseased seed. 
These may carry infection internally in the form 
of mycelia in the invaded tissue. Seed may also 
carry infection material externally in the form of 
spores or sclerotia adhering to the seed coat. 

Age of Seed. In determining the cause of poor 
germination, the age of the seed is to be considered, 
for after a certain age limit deterioration sets in. 
Each kind of seed has its own age limit, which is 
generally determined by the character of the seed 
itself, i,e,^ whether oily or starchy, or lacking in both. 
Thus the vitality of the minute seed of tobacco is 
perhaps eight times as great as that of the large oily 
seed of the castor bean. With many species of seed 
there are apparently no external symptoms to indi- 
cate loss of vitality due to age. 

Cultural Conditions, The viability of seed is also 
largely determined by the conditions undei which 
the previous crop grew. The more vigorous the 
mother plant the more vitality will there be impart- 
ed to its offspring. The vigor of the previous crop 
depends on favorable climatic conditions, care in 

104 



Germination Troubles 105 



cultivation, and in fertilization. Old seed produced 
in a favorable season may be preferred to fresh seed 
of an inferior quality produced in a bad season. 

Weight and Color of Seed. As a rule, light weight 
seed is inferior to heavy seed of the same variety. 
The weight of the seed is influenced by culture, and 
by imperfect fertilization which results in minute 
and weak embryos. The comparative weight of seed 
may be readily determined by the water method. 
Place the seed in a tumbler filled with water. After 
shaking and letting it stand for a few minutes, the 
heavier seed sink and the lighter float. Using 
this method, Stone has shown that the heavier* 
sinking seed give a higher percentage of germina- 
tion than the lighter. (See Table 15.) 



Table 15 



Name of Seed} 


No. of Seed 
: Germinated 


Per Cent, of 
Increase in 
Germination 


Light 


Heavy 


of Heavy Over 
Light Seed 




68 


90 


32 




100 


117 


17 




38 


85 


142 




44 


88 


100 




50 


58 


17 




60 


87 


61 



The color of the seed does not seem to have any 
influence on the germination. Darker colored seed 
is usually preferred to the lighter of the same va- 
riety. Color, however, largely depends on the de- 
gree of ripeness. 

♦Stone, G. E., Massachusetts Agr. Expt. Sta., Bui. 121 : 3-14, 1908. 



io6 Diseases of Greenhouse Crops 



Storage Conditions, The vitality of seed is great- 
ly influenced by storage conditions. The longest 
lived seed may be ruined by improper storage. The 
ideal conditions of storage, however, are not always 
those which favor germination. Seed should be 
cured or dried before storing. The drier it is the 
less likely it is to spoil and the higher will be the 
temperature that it can stand. When large quanti- 
ties of seed are to be handled by the trucker, it is 
advisable to build a seed house. The seeds are best 
kept in strong paper or cloth bags, placed in tin or 
galvanized iron cans. 

Seed Testing. In buying seed we must never 
take it for granted that the germination will be per- 
fect. To make sure, a sample of the seed should be 
tested for germination. The simplest method, per- 
haps, is to sow a definite number of seed in a shal- 
low pan filled with moist sand, and kept covered in a 
warm, dark place. However, the fact that a seed 
sprouts does not always imply that it will develop 
into a normal plant. Hence, allowance should be 
made for this probability when making a test at 
home or in the seed laboratory. 

Effect of Fertilizer on Seed, With the hope of 
hastening germination, greenhouse men often apply 
various fertilizers to the seed bed. This practice 
cannot be too strongly discouraged, especially when 
muriate of potash and nitrate of soda are used. 
These two fertilizers when used in strengths of one 
per cent, or more, inhibit the germination of the 
seed, whether applied directly or mixed with the 



Germination Troubles 107 



soil. Phosphoric acid or lime, when not used in 
excess, seems to have no injurious action on seed 
germination. However, on no account should com- 
mercial fertilizers be brought into direct contact with 
the seed. This is well brought out in Table 16 by 
Hicks.* 

Table 16 



Effect of Chemical Fertilizers on the Germination 
of Breakfast Radish Seed 



Fertilizer Used 


How Applied 


First Sprouts 


Per Cent, 
of Germi- 
nation 




In the rows 

Mixed with soil. . 

Mixed with soil. . 

In the rows 

Mixed with soil. . 


No sprouts 
No sprouts 
May 26 
May 24 
May 25 
May 26 
May 24 
May 24 
May 25 
May 24 
May 24 


1.5 
1-5 
10. 0 
950 
2.0 
6.5 
37.5 
930 

34.5 
92.0 

96.5 


Check, no fertilizer. . . 


Mixed with soil. . 
Mixed with soil. . 



Seed Treatment. Since seed is often a carrier of 
disease it is essential that it be treated before plant- 
ing. Treating the seed for about ten minutes with 
sulphuric acid will hasten germination and destroy 
adhering spores of disease-producing organisms. 
However, more information is needed before this 
method can be universally adopted by the green- 
house grower. In practice, the safest method would 
be to soak all seed, before planting, in a solution 

*Hicks, G. H., U. S. Dept. of Agr., Div, qf Botany, Bui. 24: 5-15, 
1900. 



io8 Diseases of Greenhouse Crops 



of one part of formaldehyde in 320 parts of water, 
i.e., one pint of formaldehyde in 22 gallons of 
water. The soaking is carried on for 10 or 20 
minutes, depending on the size of the seed and per- 
meability of the seed coat. 



CHAPTER 9 



DISEASES OF GREENHOUSE CROPS 

Asparagus (^Asparagus Officinalis) 

Cultural Considerations, Asparagus plants lend 
themselves admirably to forcing. It is now grown 
for commercial purposes on a fairly large scale in- 
doors. Light is not essential for this crop. The 
beds may be in total darkness, although a diffused 
light is preferred. Any variety which produces 
large shoots is desirable for forcing. However, the 
variety Reading Giant has been developed for its 
resistance to rust, and therefore should be given pref- 
erence. Forced asparagus may be grown in any soil, 
even sand or coal ashes, provided it contains plenty 
of organic matter. At the beginning of the forcing 
process, the temperature should not run higher than 
45 50 degrees F. for at least one week. As soon 
as strong shoots are made, a temperature of 65 to 
70 degrees is desired. In order to obtain high yields, 
profuse watering is necessary. 

Diseases of Asparagus 

Greenhouse asparagus seem to be subject to but 
few diseases. 

Damping Off, see Rhizoctonia, p. 20. 

Z09 



110 Diseases of Greenhouse Crops 

Rust (Fuccinia aspargi D.C.) seems to be of no 
importance as a disease of forced asparagus. 

Bean (Phaseolus Vulgaris^ 

Cultural Considerations, Beans are not to be 
grown as a fall or winter crop. They are produced 
more easily and more profitably as a spring crop. 
In this case they follow well a winter crop of let- 
tuce. The night temperature should not go below 
60 degrees F. The best soil for bean culture is a 
rich light sandy loam. The soil should never be al- 
lowed to become damp and cold for any length of 
time. It must not be allowed to become packed 
and soggy through overwatering. As a safe guide 
to success, the crop should never receive a check 
in its growth in any period of its development. Of 
the varieties adapted to forcing may be mentioned, 
Black Valentine, Long Yellow Six Weeks, Ken- 
tucky Wonder. 

Diseases of the Bean 

Forced beans may be attacked by several impor- 
tant diseases. 

Blight 

Caused by Pseudomonas pJiaseoli Ew. Sm. 

Symptoms. If the soil is too wet during planting 
time, the seed may rot in the ground and never ger- 
minate. At other times the roots of the young seed- 




Fig. 15. Bean Diseases. 

a. Anthracnose on pods (after Halsted), h. cross section of bean seed to show 
relationship of Colletotrichnm lindemiithianum to its host, c. cross section of 
bean seed to show canker produced from anthracnose {h-c after Whetzel), d. 
crass section of bean tissue to show presence of the bean blight organism, e. 
Pseudomonas phaseoli {d-e after Smith, E. F.). 



Bean Diseases 



III 



lings may decay and the result will be a very poor 
and uneven stand. Under drier conditions a better 
germination is obtained. The disease also works on 
the older plants, forming irregular spots. When 
their root system is attacked, affected plants become 
yellowed and wilted by daytime, but slowly revive 
at night. Should the air become muggy by over- 
watering and high temperatures, infected plants ap- 
pear as though they have been drenched with hot 
grease, the leaves having a burned appearance. The 
injured plants then seem to make a desperate at- 
tempt to produce new foliage, which in turn becomes 
affected; the pods cease filling, and ripening is very 
uneven. 

In carefully examining diseased seed, it is found 
to be yellowed and shriveled; or, in light cases of 
attack, covered with irregular yellow blotches. On 
the leaves, the trouble appears as watersoaked spots 
which later become amber colored. The cankers on 
the stems somewhat resemble the canker produced 
by Colletotrichum lindemuthianum. 

The Organism. Fseudomonas phaseoli Ew. Sm. 
is a short rod, rounded at both ends, and motile by 
means of polar flagella (fig. 15, d and e.). It lique- 
fies gelatin slowly, coagulates milk, and produces no 
gas. For methods of control, see Anthracnose, p. 112. 

SCLEROTINIA RoT 

Caused by Sclerotinia lihertiana Fckl. 
Sclerotinia rot is a disease which attacks snap 



112 Diseases of Greenhouse Crops 



beans. During a period of several hot humid days 
the disease may suddenly break out in great se- 
verity. Usually withering and decaying of stems 
and pods where the plants are thickest is the first 
symptom that attracts attention. On closely ex- 
amining infected stems and pods, we find that they 
are watersoaked, and overrun by a white mycelial 
growth on which appear numerous hard, black scle- 
rotia. In the field, the Black Valentine snap bean 
seems to be more resistant to rot. For a description 
of the causal fungus and methods of control, see let- 
tuce drop, p. 150. 

Powdery Mildew 

Caused by Erysiphe polygoni D. C. 

Symptoms, Powdery mildew is a serious bean 
disease. It is characterized by white, mealy patches 
on the surface of the leaves and stems. The foliage 
soon turns yellow and dry. Powdery mildew may 
be controlled by dusting the plants with flowers of 
sulphur. Care in the proper amount of watering and 
ventilation will also help to keep it in check. 

Anthracnose 

Caused by ColletotricJium Undemuthianum (Sacc. 
& Magn.) B. and C. 

Symptoms. Anthracnose is so characteristic that 
it cannot be mistaken for any other disease, except 
perhaps the blight. In light attacks, the seeds are 



Bean Diseases 



113 



covered with sunken brown to black specks. These 
are especially evident on the white seeded varieties. 
In severe attacks, the seeds are covered with deep 
sunken black spots (fig. 15, c.) which are rifted in 
the center. On the leaves the disease attacks the 
veins, which become blackened and somewhat 
shrunken. Frequently it attacks the petioles, espe- 
cially at the point of leaf attachment. In this case, 
the foliage drops off, leaving the bare petioles or 
stems. Anthracnose on the pods begins as small, 
circular, pin-point, dark red spots which enlarge, 
and later elongate into maroon colored pits, cracks, 
or cankers (fig. 15, a.). On young seedlings the 
stem rots off a short distance above groimd. 

The Organism, Spores are formed on the spots 
or cankers of all parts affected (fig. 15, b.). These 
are imbedded in a gelatinous substance and may be- 
come loosened only by water splashing upon it. It 
is at this stage that the disease becomes serious, for 
it is then spread from plant to plant. When the 
spores are lodged on a new bean plant or on a new 
part of the same plant, infection takes place through 
the penetration of the tube of the germinated spores. 

Control. Spraying has not given satisfactory re- 
sults. The best control is to plant clean seed select- 
ed from clean pods. The latter, before shelling, may 
be dipped for ten minutes in a solution of one part 
of corrosive sublimate to a thousand of water. The 
treated pods are then dried in the sun, shelled, and 
the seed put away in dry Mason jars until planting 
time. Should weevils threaten these seeds, they 



114 Diseases of Greenhouse Crops 



may be fumigated with carbon bisulphide. Under 
no circumstances should infected plants be syringed. 
When this is done the spores of the fungus are scat- 
tered broadcast. Recently Burkholder has suc- 
ceeded in developing a resistant bean by crossing the 
Well's Kindney Bean with the WTiite Marrow va- 
riety. 

Root Rot, see Rhizoctonia, p. 20. 
Root Knot, see Nematode, p. 28. 

Beet (Beta vulgarisy 

Cultural Co7isiderations. Beets are not grown 
very extensively in the greenhouse. They are, how- 
ever, raised on a small scale for greens or for the 
roots. It is often used as a companion crop with 
tomatoes. The Eg}'ptian or any other early variety 
is preferable. The cultural requirements of the beet 
are the same as those of the lettuce, see p. 145. 
However, beets will grow more rapidly under higher 
temperatures than lettuce. 

Diseases of the Beet 

Indoor beets are subject to less diseases than those 
grown out of doors. The following are the more 
important ones: 

Crown Gall 

Caused by Fseudomo?ias tumefaciens Sm. and 
Town. 

♦Burkholder, W. H., Phytopath. 8: 353-359, 1918. 




Fig. i6. Beet Diseases. 



a. Nematode or root knot, h. Crown gall, c. Cercospora leaf spot (after 
Halsted), d. spores of Cercospora beticola (after Schwarze). 



Beet Diseases 115 



Crown gall is a very important disease because of 
its cosmopolitan nature, for it is widely prevalent 
and attacks a large number of hosts. 

Symptoms. The disease does not usually mani- 
fest itself until the roots are nearly half grown. 
Abnormal outgrowths or galls (fig. 16, b.) appear 
which vary in size from that of a garden pea to 
nearly two inches in diameter, according to the se- 
verity of the attack. The galls are usually attached 
to the beet by a narrow string. In light cases of 
infection there may be but one gall on the root; in 
severe cases, however, the roots may be covered with 
numerous galls. 

The Organism. The cause of crown gall is a bac- 
terial organism, Fseudomonas tumefaciens Sm. and 
Town. It is a short rod, multiplying by fission, and 
moves about by means of polar flagella. On agar 
or gelatin it forms small round white colonies. Un- 
der unfavorable conditions it readily develops in- 
volution forms; the organism is short lived in pure 
culture. P. tumefaciens lives over in the soil from 
year to year. 

Control. The disease may be introduced with in- 
fected soil. Sterilizing the soil with steam or for- 
maldehyde (see pp. 32-43) is recommended. 

Scab 

Caused by Actinomyces chromogenus Gasp. 
Scab on beets is the same as the scab of the Irish 
potato, the radish, and the carrot. 



ii6 Diseases of Greenhouse Crops 



Symptoms, The symptoms of the disease on beets 
do not differ from those of the Irish potato. Occa- 
sionally, the scabs which arise before the beet is full 
grown disappear entirely, leaving merely a small 
scar. This is somewhat sunken and has a definite 
outline. In normal cases of infection, the scabby 
areas on the beet are rough; while the corky layer 
of the spots decidedly bulge out. Immediate- 
ly below them, the tissue is a discolored reddish 
brown. 

The Organism, The cause of beet scab is the 
same as that of the scab of the white potato. The 
parasite is a soil organism, and thrives best under 
alkaline conditions. 

Control, The disease is introduced with infected 
soil, or with the compost. Care should be taken 
that no infected potato peelings find their way to 
the manure pile. Soil sterilization with steam, or 
formaldehyde (see pp. 32-43) is recommended. 

Damping Off and Root Rot 

Caused by Fythium de Baryanum Hess. 

Symptoms, Damping off very commonly occurs 
just as the seedlings emerge from the ground. These 
topple over and die in the characteristic way so fa- 
miliar to truckers. The greatest damage follows 
from overwaterings, when a hard crust is formed on 
the surface, a condition which prevents the seedlings 
from emerging normally. On old and mature roots, 
Pythium de Baryanum may cause a rot. A pecu- 



Beet Diseases 



117 



liarity of this disease is that it seldom starts at the 
top of the crown. The latter appears to be perfectly 
healthy, although the leaves turn yellow, indicating 
a diseased condition further down. Rotted roots are 
found to be overrun by a varied flora, although 
Pythium is the original cause of the trouble. For a 
further description of the organism see p. 17. 

Control, The methods of controlling this dis- 
ease are the same as those for lettuce drop, see p. 151. 

Downy Mildew 

Caused by Peronospora schachtii Fckl. 

This disease is of little economic importance in 
the United States. The trouble, however, is preva- 
lent in Europe. The mildew attacks the young seed- 
lings in grayish patches on the under side of the 
foliage. On older plants, the mycelium of the causa- 
tive fungus works downwards into the root, causing 
it to rot. 

Drop 

Caused by Sclerotinia lihertiana Fckl. 

Drop, which attacks young seedlings of the beet, 
but not the older plants, is not very different from a 
similar trouble on lettuce. The high temperature of 
the soil soon after making the hot bed, is important 
in favoring the disease. Sterilizing the soil with 
formaldehyde, careful regulation of temperature, 
and watering are methods to be observed in the con- 
trol of the trouble. 



Ii8 Diseases of Greenhouse Crops 



Leaf Spot 

Caused by Cercospora heticola Sacc. 

There is perhaps no beet disease that is of greater 
economic importance than leaf spot. The trouble 
is well known to truckers and it seems to be found 
wherever beets thrive. 

Symptoms. The disease first makes its appear- 
ance on the leaves as tiny circular whitish spots. 
These gradually increase in size and assume a brown- 
ish color. The spots soon multiply and involve the 
entire leaf area (fig. 16, c), which becomes dry and 
brittle. Leaf spot attacks the outer and older leaves 
first. As the inner foliage advances in age, they too 
become infected in turn. Serious though the dis- 
ease may appear, it never kills the plant. The re- 
sult, however, is noticeable on the roots, which are 
undersized and elongated instead of round. Leaf 
spot generally appears in overwatered and poorly 
ventilated houses. The disease increases in severity 
as the plants are weakened by heat. 

The Organism. The fungus, Cercospora heticola^ 
Sacc, like most fungi, is composed of a vegetative 
part of mycelium and of spores. The latter are 
microscopic in size, somewhat needle-shaped, and di- 
vided by means of a cross wall into cells numbering 
from two to seven (fig. 16, d.). Each of these cells 
may germinate by sending out a thread-like tube, 
which penetrates the leaves through the stomata. 
The spores are borne on a cluster of stalks or conidio- 
phores, at the base of which is formed a small 



Beet Diseases 



119 



Stroma. The temperature and relative humidity of 
the air influence the production and infection of 
conidia. Conidia are generally formed on the lower 
surface of the leaves, no doubt because these are 
subject to a higher humidity. 

Control. Infected material should be destroyed 
by fire. Spraying with Bordeaux mixture 4-4-50 is 
also recommended. 

Root Rot 

Caused by Rhizoctonia solani Kuhn. 

Symptoms. This disease produces a damping off 
of the young seedlings, and on older plants a rotting 
of the crown. Upon pulling out an infected plant, 
we find that the outer leaves are dead and dry, while 
the inner ones are somewhat curled. The roots of 
such plants invariably are rotted at the crown, the 
rot generally working inwards to a considerable ex- 
tent. The peculiarity of this disease is that the 
lower half of the root is generally sound. Frequent- 
ly, the rotted crowns are also found to be cracked 
at various places. Beets thus affected are worthless 
for the market. For a description of the fungus 
see p. 20. 

Control. There are no methods of control known. 
The factors which favor the trouble are poor drain- 
age, an excess of soil moisture, and lack of suffi- 
cient ventilation. Every step taken to overcome 
these will in a degree help to control the rot. Soil 
sterilization is also recommended. 

Root Knot, see Nematode, p. 28 (fig. 16, a.). 



120 Diseases of Greenhouse Crops 



The organisms Pseudomonas teutlium Met., Vs, 
beticola Ew. Sm., Urophlyctis leproides (P. Mag.) 
Trab., Cystopus blitz (Biv.) Lev., Uromyces hetcz, 
Kuhn, and Phoma bet(Z Fr. seem to attack beets 
out of doors only. 

Carrot {Daucus carotd) 

Cultural Considerations. Carrots are forced in 
about the same way as the radish. The soil, how- 
ever, should be more sandy. The variety best adapt- 
ed for forcing is the early small topped Short Horn 
type. 

Diseases of Carrots 
Carrots are very hardy and subject to but few 
diseases of consequence. 

Soft Rot, see Cauliflower, p. 126. 
Root Rot, see Rhizoctonia, p. 20. 

Cauliflower {Brassica oleracea var. botrytis^ 

Cultural Considerations, Cauliflower is not so 
extensively forced because large amounts of it are 
shipped from California during the forcing season. 
Nevertheless, indoor cauliflower is far superior in 
quality, and with the proper advertisement the 
forced product should gain greater recognition 
from the consumer. There are few varieties which 
lend themselves well to forcing. The Snowball and 
the Erfurt are preferred by most growers. The soil 



Carrot Diseases 



121 



should not be too heavy, although the plants are 
heavy feeders. The compost should contain a fair 
amount of well rotted manure. In addition, a well 
balanced fertilizer may be added at the rate of 
1,000 pounds per acre. Lime should also be added 
to the beds at least once every two years. This will 
sweeten the soil in case it has a tendency to sour. 
Cauliflower requires an abundance of water. Lack 
of sufficient water may check the growth, an effect 
that will result in small or no heads. On the other 
hand, overwatering may produce an excess of foliage 
at the expense of head development. In warm 
weather, the plants and the walks should be syringed 
in order to keep the atmosphere moist. The best 
night temperature is about 50 to 55 degrees F. and 
the day temperature from 65 to 70 degrees. Plenty 
of ventilation should be provided; but drafts should 
be avoided. 



CHAPTER lo 



DISEASES OF CAULIFLOWER 

Indoor cauliflower seems to be subject to less dis- 
eases than that grown out of doors. The troubles 
which attack this plant are practically the same as 
those which are found on the cabbage. 

Club Root 

Caused by Flasmodiophora bras sic ce Wor. 

Symptoms. Affected plants show a wilting of the 
foliage in the day, although recovering in the eve- 
ning or during cloudy weather. Diseased plants are 
dwarfed, pale, and sickly looking. The seat of the 
trouble is at the roots. The latter swell considerably 
in size, often taking on the form of a hernia (fig. 17, 
a-c). The disease is more severe on seedlings in the 
seed bed, from whence it is carried to the field or to 
the greenhouse. 

The Organism. Club root is caused by a slime 
mold. The spores of the parasite (fig. 17, d.) are 
nearly round and possess a transparent and refrac- 
tive cell wall. The first signs of germination are a 
swelling of the spores, followed later by a bulging 
at one side. The inner pressure exerted splits the 
spore wall, thus permitting the protoplasm (swarm 

122 



Fig. 17. Cauliflower Diseases. 



a. Young cauliflower plant with club root (after Jones, L. R.), h. cross 
section of an infected root, c. cross section of a young healthy root (b-c after 
Woronin), d. host cell containing Myxomycete spores (after Lutman, B. F.). 



Cauliflower Diseases 123 



spores) to ooze out. The latter is without a cell 
wall, and moves by means of a thick flagellum at the 
small end. The germination of the spores is im- 
proved by exposing them for a short time to cold and 
drying. The best medium is water which has been 
filtered through muck soil. 

Infection of the hosts takes place through the 
wall of the root hair while the organism is in a uni- 
nucleate stage. Entrance of the parasite is evi- 
denced by the browning and shriveling of the root 
hair. 

Control. If this disease becomes introduced into 
the greenhouse, the safest course would be to ster- 
ilize the soil in the benches and in the seed bed. 
Sterilization with steam or formaldehyde is recom- 
mended (see pp. 32-43). 

Bacterial Leaf Spot 

Caused by Fseudomonas maculicolum McC. 

Symptoms, The disease is characterized by nu- 
merous small brownish to purple-gray spots. When 
the small spots coalesce, the entire leaf surface may 
be involved. Practically all parts of the leaves are 
affected. When the midribs and veins are attacked, 
the tissue becomes shrunken, and the leaves have a 
puckered appearance. In the early stages of infec- 
tion, the spots on the leaves are watersoaked, later 
they become dry and turn dark merging into pur- 
plish gray. In transmitted light, the centers of the 
spots are thin, almost colorless, and are surrounded 



124 Diseases of Greenhouse Crops 



by a dark border. The diseased leaves become yel- 
low and drop off prematurely. The trouble appar- 
ently does not attack the cauliflower head. The same 
disease may also attack the radish. 

The Organism. The disease is produced by Fseu- 
domonas maculicolum^ a rod-shaped organism, with 
rounded ends, usually forming long chains in cer- 
tain media, but producing no spores. The organism 
is actively motile by means of polar flagella. Invo- 
lution forms are produced in alkaline beef bouillon; 
and pseudo-zoogloeae occur in acid beef bouillon. 
No gas is produced and the organism is aerobic. It 
is killed by drying and exposure to light. 

Control. Badly diseased plants should be pulled 
up and destroyed. Spraying with 4-4-50 Bordeaux 
is recommended. In spraying cauliflower with cop- 
per compounds, and especially if the latter are in a 
concentration somewhat stronger than the plant can 
stand, numerous warts will appear on the leaves in 
about three days after spraying. These warts should 
not be mistaken for a disease induced by a parasitic 
organism. The wart formation is apparently due 
to a stimulation from the salts absorbed by the host 
cells. 

Black Rot 

Caused by Pseudomonas campestris (Pammel) 
Ew. Sm. 

The disease is known both as stem rot and black 
rot. The latter perhaps is the more common name. 
Symptoms. Black rot has distinct symptoms 



Cauliflower Diseases 125 



which cannot easily be confused with other diseases. 
On the leaves, the symptoms are manifested as a 
burning appearance on the edges and a yellowing 
of all the affected parts except the veins, which re- 
main blackened. From the margin of the leaves, the 
disease works downwards to the stalk. From there 
it travels up again to the stems and leaves. The 
parasite works in the fibrovascular bundles of the 
leaves and main stalk, causing a premature defoli- 
ation. Occasionally, the disease enters one side of 
the stalk, the latter becoming dwarfed and the cauli- 
flower head grows one-sided. In severe cases of 
attack, there is a total lack of head formation. Upon 
splitting open a stump of an affected plant, one finds 
a black ring which corresponds to the places of the 
fibrovascular bundles invaded by the organism. In- 
fection takes place through small openings naturally 
found on the leaves and known as water pores which 
are scattered over the teeth of the leaves. Infec- 
tion by means of insect bites is also a very common 
occurrence. Outbreaks of black rot may undoubt- 
edly be traced back to the use of infected manure. 
Black rot also attacks greenhouse radish. 

The Organism, Fseudomonas campestris is a rod- 
shaped organism, slightly longer than it is broad. 
When young it is actively motile by means of long 
polar flagella. It is found single or in pairs and 
produces no spores. It liquefies gelatine completely 
in about ftfteen days. On agar plates the colonies 
are round, yellow in color, and the margin entire. 



126 Diseases of Greenhouse Crops 



On potatoes a liberal growth is produced with no 
odor and no browning of substance. 

Control, Before planting, cauliflower seed should 
be disinfected for fifteen minutes in a solution of 
J4 pint of pure (40%) formaldehyde diluted in 
seven gallons of water. In making the seed bed, 
manure known to be free from cabbage refuse should 
be used. All insect pests should be kept in check 
by spraying with arsenate of lead. The disease can- 
not be controlled by merely cutting off diseased 
foliage. If anything, this operation aggravates the 
trouble. Diseased plants should be pulled out and 
destroyed. 

Soft Rot 

Caused by Bacillus caratovorus Jones. 

Soft rot, although a field trouble, causes consid- 
erable damage to greenhouse cauliflower. 

Symptoms. The disease is characterized by ^ soft, 
mushy to slimy decay of the entire plant. The dis- 
ease works very rapidly under favorable conditions 
of moisture and temperature. The causal organism 
can gain entrance only through a wound or bruise. 

The Organism. Soft Rot is caused by a bacillus 
that is rod-shaped, of varying length, and usually 
formed in chains. It moves about by peritrichous 
flagella. It completely liquefies gelatine in about 
six days. Gas is produced with a majority of strains. 

Control. Diseased plants should be destroyed by 
fire. To check further spread, water should be with- 
held and plenty of ventilation allowed. During 



Cauliflower Diseases 127 



watering unnecessary splashing of soil particles on 
the plants should be avoided. 

Damping Off 

Caused by Olpidium hrassiccz (Worr.) Dang. 

The symptoms of damping off for cauliflower are 
similar to those produced by Pythium de Baryanum^ 
p. 17. The sporangia of the parasite may be found 
singly or in groups in each infected host cell. The 
zoospores are globose, uniciliate. The resting spores 
are globose, wrinkled, and star-like in appearance. 

The disease is found mostly in seed beds, where 
it does considerable damage. For methods of con- 
trol, see pp. 32-34. 

Downy Mildew 

Caused by Feronospora parasitica (Pers.) De By. 

Symptoms. Downy mildew, while a common field 
disease, causes considerable damage to young seed- 
lings in the seed beds. It is characterized by whit- 
ish downy patches on the underside of the leaf. Seen 
from above, the affected areas are angular, pale yel- 
low, and somewhat shrunken. The spots seem to be 
limited by the veins of the leaves. The disease is 
common in damp houses. Besides the cauliflower, 
the radish, and numerous other cruciferous hosts are 
known to be susceptible to downy mildew. 

The Organism, The sporophores of the fungus 
are stout and numerously branched, each of these re- 
peatedly forked. The tips of the smaller branches 



128 Diseases of Greenhouse Crops 



are slender and curved. The conidia are broadly 
elliptical, and the resting spores are globose and 
smooth, becoming wrinkled with age. 

Control. In the seed bed, spraying with 4-4-50 
Bordeaux will control the disease. The first applica- 
tion should be given as soon as the disease makes its 
appearance. Later the application will be governed 
by disease conditions. Care should also be taken 
to avoid sowing the seeds too thickly. Overwater- 
ing, poor ventilation, and high temperature favor the 
disease. 

Drop 

Caused by Sclerotinia Uhertiana Fckl. 

Drop is a disease fairly common on cauliflower. 
The trouble may be recognized by a drooping and 
wilting of the leaves. The bases of the affected 
foliage are covered with a white weft of mycelial 
growth, later by sclerotia. For a more extended 
discussion of the disease, see lettuce drop, p. 1 50. 

Ring Spot 

Caused by MycosplKzrella hrassiazcola (Duby) 
Lind. 

Symptoms. On the leaves, the disease appears 
as numerous small spots and the affected foliage 
turns yellow. Most of the spots are formed on the 
laminse, but others are also formed on the large 
midribs. The spots are definite in outline, round 



Cauliflower Diseases 129 



and visible on both surfaces of the leaf. The 
color is light brown to gray, with dry centers 
surrounded by olive green or blue green borders 
which shade off into the natural color of the leaf. 
The outer edge of the spot is covered with the fruit 
of the fungus. Spraying with 4-4-50 Bordeaux is 
recommended. 

Black Mold 

Caused by Alternaria bras sic cz (Berk.) Sacc. 

Affected leaves are covered with spots which arc 
nearly black on the under side of the leaf. The spots 
are composed of a series of rings, the smaller ones 
enclosed within the larger. There is no distinct 
border separating the diseased portions from the 
healthy; the spots gradually shade off into the 
healthy tissue. Little is known of the causative 
fungus or of the control of this disease. It is prob- 
able that spraying with 4-4-50 Bordeaux will be of 
value. 

Root Knot 

Caused by Heterodera radicicola (Greef) Mull. 

Root knot is characterized by small swellings on 
the lateral feeding roots. For a description of the 
parasite and methods of control, see p, 28. 

Celery (^Apium graveolens) 

Cultural Co7isideratio7is. Celery has not yet taken 
its place among the standard forced vegetables. It 



130 Diseases of Greenhouse Crops 



is possible, however, to produce celery in the green- 
house which is of a quality far superior to that grown 
out of doors. The self-bleaching varieties such as 
the Kalamazoo seem to be well adapted for forcing. 
The White Plume seems to have a tendency to go 
to seed, and the Golden Self-blanching is subject to 
heart rot. Celery requires an abundance of mois- 
ture. A lack of it will cause such a setback to the 
plants that they may never recover. Too high or 
too low a temperature has the same detrimental 
effect. 

Diseases of the Celery 

Celery is subject to numerous diseases. Success 
with the crop demands great care in the production 
of healthy plants. 

Soft Rot, see Cauliflower, p. 126. 

Late Blight 

Caused by Septorza petroselini Desm. var, apii Br. 
and Cav. 

Symptoms. The disease first attacks the lower 
leaves of the stalk, producing irregular spots with- 
out a definite boundary line. When the spots be- 
come numerous the foliage withers and dries up 
(fig. 18, a.). The disease attacks the leaves as well 
as the stalks, rendering the affected plants useless 
for the market. In storage, plants affected with late 
blight will keep very poorly or rot altogether. 

The Organism, The fungus mycelium is hyaline, 




Fig. i8. Celery Disease. 

a. Septoria leaf spot, b. cross section through leaf to show relationship of 
fungus to its host, c. spores of Septoria petroselini (a-c after Coons). 



Celery Diseases 



131 



septate. The pycnidia (fig. 18, b.) are olivaceous, 
prominent, and abundant in the spots. The pycnio- 
spores are filiform, straight or curved, hyaline and 
many are septate (fig. 18, c). 

Control, According to Rogers,^ late blight may 
be controlled by spraying with 5-6-50 Bordeaux. 

The first two applications should be given 
to the seedlings in the seed bed. In the house 
the first spraying should be administered about six 
weeks after transplanting. Besides spraying, shad- 
ing also seems to keep the disease in check. In 
spraying celery, great care should be exercised to ap- 
ply a fine mist. Where this is overlooked, large 
drops of the Bordeaux mixture may be deposited 
on the leaves and stalks, which upon drying may 
deposit copper salt in sufficient quantity to injure 
the consumer. Sprayed celery should be carefully 
washed and dried before shipping. 

Early Blight 

Caused by Cercospora apii Fr. 

Symptoms. The trouble first appears on the 
outer leaves as pale blotches visible on both sides 
of the affected parts. The spots are irregular, an- 
gular in outline, limited apparently by the leaf veins, 
with slightly raised borders (fig. 19, a.). The spots 
later turn brown to ashy white. 

The Organism. The conidiophores are usually 

*Rogers, S. S., California Agr. Expt. Sta. Bui. 208: 83-115, 191 1. 



132 Diseases of Greenhouse Crops 



borne on the under side of the leaf, light brown, and 
in clusters. The conidia are hyaline, 3 to lo septate, 
cylindric (fig. 19, b.). 

Control, Early blight as well as late blight may 
be controlled by spraying with Bordeaux mixture. 
The Boston Market and Golden Heart varieties 
should be avoided because of their susceptibility to 
the disease. The White Plume seems to be resist- 
ant. 



CHAPTER 11 



CUCUMBER (Cucumis sativus) 

Cultural Considerations, Cucumbers are exten- 
sively forced for the winter or early spring markets, 
(fig. 20.) The houses generally used are either 
two-thirds or even-span and are provided with 
ground beds instead of benches. 

Unlike lettuce, cucumbers are not so sensitive to 
variations in soil texture. A great variety of soils 
may be used if, however, they are well provided with 
organic matter. Cucumbers require a night tempera- 
ture of about 65 degrees F. and about 85 degrees 
during bright weather. In cloudy weather, how- 
ever, the day temperature should be about 10 to 15 
degrees lower, otherwise the plants will become 
weak, spindly and susceptible to disease. Extreme 
care is required in watering the plants. Overwater- 
ing during cool, wet weather will greatly injure them 
by encouraging numerous diseases. 

Of the varieties which lend themselves to forcing 
are the Telegraph (English), and all strains of Dark 
Spine and White Spine among the American varie- 
ties. 

Diseases of the Cucumber 

Cucumbers under glass are subject to a large num- 
ber of diseases. 

133 



134 Diseases of Greenhouse Crops 



Leaf Curl 
Cause, physiological. 

Symptoms, The trouble is often manifested as a 
wilting of the edges of the leaves which curl into a 
spherical form. The wilted area soon dies, thus 
preventing any further development of the affected 
leaf. As the inner part of the leaf continues to grow 
and as it is restricted by its outer dead area, it as- 
sumes a convex form and a contorted margin, so 
that it curls up and assumes the shape of a ball. 
In advanced cases the stems, too, curl. The disease 
was studied by Stone who believes that the cause 
of the trouble is overmanuring. Abnormal modifi- 
cations in the light, soil texture, and moisture condi- 
tions may frequently induce the same trouble. To 
prevent this disease the use of excessive manures 
should be avoided. As far as possible, conditions 
which favor weak soft growth should be eliminated. 

Malnutrition of Cucumbers 

Cause, physiological. 

Malnutrition generally results from an overfer- 
tilization of the soil. This trouble has been care- 
fully studied by Haskins f who found it very preva- 
lent on indoor cucumbers. 

* Stone, G. E., Mass. (Hatch) Agr. Expt. Sta., Bui. 87: 3-43, 
1903. 

t Haskins, H. D., Mass. Agr. Expt. Sta. Twenty-fifth Ann. Kept.: 
71-76, 1913. 



Cucumber Diseases 135 



Symptoms. At first, the plants have a vigorous 
appearance, but soon turn yellow and fail to form 
fruit. The leaves of affected plants become spotted^ 
resembling somewhat mosaic. 

Cucumbers are often grown in the same beds for 
a number of years. Each year as new manure and 
fertilizers are added, the salt content of the soil 
becomes higher and more concentrated. Although 
there is an abundance of available food in the soil, 
the cucumber suffers because it is unable to stand a 
concentrated form of food. Chemical analysis of 
a normal and an overfed soil throws much light on 
this important subject. These analyses are given 
in the accompanying Table 17. 



Table 17 

Average Composition of an Overfed Soil Com- 
pared with Normal Soil 





Founds per Acre 




Overfed Soil 


Normal Soil 




27-363 


7.520 




1. 156 


444 




6.743 


1-328 




632 


208 




1 .211 


864 




3-259 


1 .624 




966 


320 




1.240 


727 



From Table 17 it is seen that an overfed soil has a 
marked increase of soluble plant food. If we should 
express this in terms of fertilizers it would make 3^ 



136 Diseases of Greenhouse Crops 

tons of nitrate of soda, 6^ tons of high grade sul- 
phate of potash, 2 tons of 16 per cent, phosphate, 
and 1 ton of hydrated lime. To express it in terms 
of a mixed fertilizer it would amount to 14^ tons 
of a formula testing 4 per cent, nitrogen, 23 per cent, 
actual potash and 2.25 per cent, available phosphoric 
acid. The injurious effect on cucumbers is not due to 
the excess of any one element but rather to the toxi- 
city of the combined excess of soluble salts. 

Physiological Wilt 

Symptoms, Cucumber growers often find that 
their plants wilt badly when subjected to the in- 
tense rays of the sunlight. This is especially true 
when bright weather follows a continued cloudy 
spell. This trouble is common in houses which are 
poorly ventilated, and where the plants are weak. 
Too high a temperature and poor lighting will great- 
ly favor wilting. The removal of these causes will 
effect a cure. 

Lack of Color in Fruit 

Cucumber fruit, especially of the White Spine va- 
riety, often becomes very white, thus commanding a 
lower market price. This discoloration is probably 
due to a lack of available nitrogen in the soil. It 
may be remedied by the application of one part 
liquid nitrate of soda to one thousand parts of water. 



a 









e 




b 



Fig. 21. Cucumber Diseases. 

o. Mosaic, anthracnose. 



Cucumber Diseases 137 



Mosaic or "White" or "Little Pickle" 
Cause unknown. 

Symptoms, The first sign appears as a yellow 
mottling near the stem end of the fruit. Later the 
light areas are found all over the cucumber, and 
the darker portions frequently form protuberances. 
Some fruits retain their green color and show the 
disease only by being distorted. The leaves become 
mottled light to dark green (fig. 21, a), and some- 
times wrinkled, while the stems and petioles are 
dwarfed and distorted. Affected leaves die prema- 
turely and are replaced by others, which in turn con- 
tract the disease. The trouble is spread principally 
by the melon louse. Aphis gossypii Glov., and to a 
lesser degree by striped cucumber beetle, Diabrotica 
vittata Fabr. Satisfactory methods of control are 
still wanting. Affected plants should be destroyed 
to prevent further spread of the disease. 

Bacterial Wilt 

Caused by Bacillus tracheiphillus Ew. Sm. 

The symptoms and the damage caused by this 
wilt will be found discussed under the muskmelon, 
p. 155. Recent investigations by Rand and En- 
lows * have shown that seeds from diseased plants 
fail to reproduce wilt. This is true not only for 
the cucumber, but also for all the other cucurbit 

*Rand, F. V., and Enlows, E. M. A., U. S. Dept. of Agr. Jour. 
Agr. Research, 6: 417-434, 1916. 



138 Diseases of Greenhouse Crops 

hosts which are subject to this trouble. Of the nu- 
merous varieties of cucumber, none shows promise 
of resistance to the disease. 

Angular Leaf Spot 

Caused by Pseudomonas lachrymans Sm. and Bry. 

Symptoms. The trouble is characterized by an- 
gular brown spots which tear or drop out when dry, 
giving a ragged appearance to the infected leaves. 
In the early stages of the disease a bacterial exudate 
collects in drops on the lower surface of the spots. 
This usually dries up and becomes whitish. It seems 
that angular leaf spots usually attack only the foli- 
age, rarely the fruit. 

The Organism, The parasite is a short rod with 
rounded ends, occurring singly or in pairs with a 
decided constriction, and occasionally in chains of 
twelve individuals or more. It is motile by means 
of polar fiagella, produces capsules on agar and milk; 
no spores, and no gas is formed. The organism com- 
pletely liquefies gelatine in about three or four 
weeks. Little is known of methods of control. 

Damping Off, see Pythium, p. 28. 

Downy Mildew 

Caused by Fseudoperonospora cuhensis (B. and 
C.) Rost. 

Symptoms, The disease appears on the leaves 



Cucumber Diseases 139 



as yellowish spots, which have no definite outline. 
In a warm, moist atmosphere numerous spots coal- 
esce, and soon the affected leaves turn yellow and 
die. With cool temperatures, the spots seem to 
spread less rapidly. The disease appears to work on 
the older leaves, beginning on those at the center of 
the plant and working outwards. With infected 
plants the center of the hill is clearly marked by a 
cluster of yellow leaves. Diseased plants may 
flower profusely, but set no fruit. The few cucum- 
bers which are set are small, deformed, and unfit for 
the market. 

The Organism. The fungus derives its food from 
the host cells by means of suckers or haustoria. The 
mycelium is hyaline, non-septate; the conidiophores 
arise in small clusters through the leaf stomata and 
are branched and flexuous. The zoosporangia are 
hyaline but slightly violet, tinted in mass. Germina- 
tion of zoosporangia is by means of motile zoospores. 
The zoospores or sexual fruiting stage was first 
found on the host by Rostovtsev. 

Control. Downy mildew seems to be most prev- 
alent on greenhouse cucumbers planted in August. 
Those set in October seem to be free from it. Where 
the disease makes its appearance, it is advisable not 
to syringe the plants, but on the other hand to keep 
the foliage dry. Diseased plants or parts of plants 
should be destroyed by fire. Late planting in Sep- 
tember or October wherever practicable is also ad- 
vised. 



140 Diseases of Greenhouse Crops 



Timber Rot 

Caused by Sclerotinia lihertiana Fckl. 

Symptoms. The disease seems to attack the stem 
end of the plant nearest to the ground line. Af- 
fected stems at first water-soaked, then become 
invaded with a cushion of white mycelial growth. 
Rapid wilting, with no recovery, immediately fol- 
lows. As the affected plant dies, the shriveled stem 
becomes covered with black masses of fungous 
bodies, sclerotia. The same fungus also causes 
lettuce drop. For a description of the causal or- 
ganism and methods of control, see p. 151. 

Powdery Mildew 

Caused by Erysiphe cichoracearum D. C. 

Powdery mildew of cucumbers is not a serious 
greenhouse trouble. Like all powdery mildews, the 
causative fungus grows on the surface of the leaf, 
giving it a white mealy appearance. From the 
mycelium are produced erect threads which bear the 
summer spores of the fungus. The ascus or winter 
stage appears as minute dark-brown, rounded cap- 
sules enclosing a group of spore sacs within which are 
formed the ascospores. 

Control. The conditions which favor mildew are 
overwatering, lack of ventilation, lack of light, and 
too high a temperature. Proper attention to these 
factors will help to remove the cause and to effect 
a cure. 



Fig. 22. Cucumber Root Knot. 



Cucumber Diseases 141 



Anthracnose 

Caused by CoUetotrichum lagenarium (Pass.) Ell. 
and Hals. 

Symptoms. This disease is often serious on green- 
house cucumbers and muskmelons. It is seldom so 
in the fall and winter, but is most frequently met 
with in the spring of the year. Affected plants 
dry up and present a parched appearance. The dis- 
ease also attacks the cucumber leaves, forming round 
spots (fig. 21, b.), and on the fruit, deep cank- 
ers, thus ruining its market value. It is claimed by 
practical greenhouse men that the great difference 
in temperature between day and night, which is un- 
avoidable in the spring when the fires have gone 
out, favors infection. 

The Organism. In structure, CoUetotrichum la- 
genarium resembles the organism of bean anthrac- 
nose. The cucumber fungus has a peculiar ability to 
remain dormant during the dry weather; but it is 
easily revived by moisture. The fruits of the fun- 
gus are borne in masses on the pustules which take 
on a salmon color. The spores are typical of all 
Colletotrichums — that is, oval, one-celled, and hya- 
line. The setse in C. lagenarium are not very plenti- 
ful. In pure culture it resembles C. lindemuthia- 
num; however, pathologically it is distinct from the 
latter, since numerous attempts by the writer and 
by others have failed to infect growing bean plants 
with the watermelon anthracnose or the watermelon 
with that of the bean. 



142 Diseases of Greenhouse Crops 



Control. As soon as the disease makes its appear- 
ance the foliage should not be syringed, but kept 
dry. Spraying with 3-5-50 Bordeaux is recom- 
mended. 

Root Knot, see Nematode, p. 28 (fig. 22). 

Eggplant {Solatium melongena) 

Cultural Considerations. Eggplants require as 
much heat as cucumbers. The night temperature 
should never run down below 60 degrees F. The 
day temperature may safely be maintained at 80 
degrees or more, provided, however, sufficient ven- 
tilation is allowed. The best soil for greenhouse 
eggplants is a light sandy soil containing plenty of 
organic matter. Raised benches with bottom heat 
is preferred for winter forcing. The eggplant does 
not thrive under an excess of water. To obtain 
marketable fruit, the blossoms must be hand pol- 
linized to insure fertilization. 

Diseases of Eggplants 

Eggplants are subject to numerous diseases. 
Southern Wilt, see Tomato, p. 185. 
Damping Off, see Pythium, p. 17. 

Fruit Rot 

Cat%d by Phomosis vexans (Sacc. and Syd.). 
Symptoms. Fruit rot attacks all parts of the plant 




a. Phomosis spot on leaf, h. pycniospores, c. conidio- 
phores, d. stylospores {b-d after Harter, L. L.). 



/ 

Eggplant Diseases 143 

except the roots. On the seedlings it cau-ses a damp- 
ing off. Young plants are attacked at the stem end 
or an inch or two above the ground line as indicated 
by a constricted area at that place. On the leaves 
the trouble is manifested as large brown round spots 
which later become irregular and ragged (fig. 23, 
a.). The older spots are light purple in the center 
and are surrounded by a black margin. As they en- 
large the spots also invade the veins, midribs, and 
petioles, forming depressions. Diseased fruits are 
at first soft and mushy, but later become dry, shriv- 
eled, and mummified (fig. 24, a.). 

The Organism, Pycnidia are usually found on 
all parts of the attacked plant. Within the body 
of the pycnidia and intermixed with the conidio- 
phores (fig. 23, c.) and pycniospores (fig. 23, b.) are 
found filiform hooked-shaped bodies termed stylo- 
spores (fig. 23, d.). Phomosis vexans has been erro- 
neously referred to as Phoma solani Hals; Phoma 
vexans Sacc. and Syd., and Aschochyta hortorum 
Speg. 

Control. The seedlings in the seed bed should be 
sprayed with Bordeaux at least once before trans- 
planting. The plant in the house should be sprayed 
from four to eight times with either Bordeaux mix- 
ture or ammoniacal copper carbonate. 

Anthracnose 

Caused by Gloesporium melengone^ E. and H. 
Anthracnose on the eggplant attacks only the 



144 Diseases of Greenhouse Crops 



fruit. The trouble is characterized by numerous 
deep pits which later become covered with salmon 
colored accrvuli (fig. 24, b.). The latter arc made 
up of myriads of spores of the fungus. Spraying for 
fruit rot will also help to control anthracnose. 
Root Knot, see Nematode, p. 28. 




Fig. 24. Egg Plant Diseases. 

a. Phomosis on fruit, b. anthracnose on fruit. 



CHAPTER 12 



LETTUCE {Lactuca sativd) 

Cultural Considerations. Lettuce is extensively 
grown as a greenhouse crop (fig. 25). The best re- 
sults are obtained where the soil contains consider- 
able sand, especially where head lettuce is produced. 
This is also true for Coss lettuce. However, the 
Grand Rapids variety will thrive in any soil. Let- 
tuce is a heavy feeder, hence stable manure is often 
used exclusively. If the crop does not make rapid 
headway, nitrate of soda at the rate of one pound 
to 100 square feet of space may be applied. In 
using acid phosphate or potash only small quantities 
should be applied for fear of burning the plants. 
Lettuce requires an abundance of water and good 
drainage. High temperatures and humidity will 
produce weak, spindly plants. Careful ventilation 
may be the cause of preventing numerous diseases. 
In mild weather the ventilators may remain open 
even at night. This, however, should not be done 
during freezing weather. 

It is fortunate that lettuce seed retains its vital- 
ity for three or four years. This enables the grower 
to test out carefully the strains which he uses. 

145 



146 Diseases of Greenhouse Crops 



Diseases of Lettuce 
Top Burn 
Cause, physiological. 

Symptoms. In plants suffering from top burn a 
withering of the leaves is followed by the curling 
back of the tips and margins of the outer leaves, the 
affected areas becoming blackened to a distance of an 
inch or more from the margin. The condition great- 
ly disfigures the lettuce head and reduces its mar- 
ket value. 

Causes. The trouble may originate on a bright 
day following a cloudy spell. The greenhouse air 
is then saturated with moisture and consequently 
the lettuce leaves transpire very little. With the 
sudden appearance of strong sunlight, there is a 
rise in temperature, and a loss of moisture in the 
greenhouse air. Under these conditions, the foliage 
will transpire heavily. If the water given off by 
the leaves is greater than the roots are able to re- 
place, the leaves will wilt, and if this is continued 
for any length of time, the tissue along the leaf 
margin will wither and die. 

ControL A practical remedy for top bum is to 
saturate the greenhouse air with moisture on bright 
days which follow cloudy spells. This will prevent 
the undue transpiration of the leaves and its subse- 
quent bad effect. 



Lettuce Diseases 147 



Bacterial Blight 

Caused by Fseudomonas viridilividum Br. 

Symptoms, The disease seems to attack only the 
outer leaves of a head. The affected foliage is first 
covered with numerous watersoaked spots which en- 
large, fuse together, and involve the entire area of 
the affected leaves. The latter either soften or dry 
up, opening up the way for the entrance of other 
decay organisms, which may now attack the other- 
wise sound head. 

The Organism is rod-shaped, occurring singly, in 
pairs, or in chains, and it moves about by means of 
polar flagella. On agar, the young colonies are round 
with entire smooth margins; they are translucent, 
cream white in reflected light, but bluish in trans- 
mitted light. The older colonies are not always uni- 
form in color, but may take on yellowish bands or 
become mottled. The organism does not form gas 
and it liquefies gelatine slowly. It is not especially 
sensitive to sunlight. 

Control. Since the disease may be introduced 
with infected soil, soil sterilization is recommended. 

The South Carolina Disease 

Caused by Fseudomonas vitans Br. 

Symptoms. The disease may attack the stems or 
leaves. At first, diseased plants become pale and 
lose their normal green. Later the head wilts and 
rots (fig. 26, a.). The rot may be confined to the 



148 Diseases of Greenhouse Crops 

outer leaves, or involve the whole head. Affected 
stems become brittle and may be readily broken. At 
first they are a blue green afterward becoming brown. 
The disease is met with in the field, but may also be 
introduced in the greenhouse. 

The Organism, Nellie Brown ^ has definitely 
proved that Pseudomonas vitans is the cause of the 
trouble which seems so prevalent in South Carolina. 
The causal organism is a short rod with rounded 
ends, motile by means of polar flagella (fig. 26, b.), 
one at each end; produces no spores, but capsules 
and pseudozoogloese. It liquefies gelatin slowly and 
produces no gas. 

Control. The disease may be introduced with in- 
fected seedlings or soil. For the latter, soil steriliza- 
tion with steam or formaldehyde is recommended. 
Diseased seedlings should be discarded. 

The Kansas Disease 

Caused by Pseudomonas marginale Br. 

Symptoms, The disease seems to appear when the 
plants are half grown. At first the leaves wilt 
slightly in restricted areas at the margin. On the 
older leaves wilting starts at the tips. The affected 
areas fall over and gradually dry up. The vascular 
tissue then becomes affected and brown, then 
reddish, and finally black. The tissue of the 
dead parts on the leaves becomes dry and papery. 

♦Brown, Nellie A., U. S. Dept. of Agr., Jour. Agr. Research, 13: 
367-388, 1918. 



Fig. 26. Lettuce Diseases. 



a. Bacterial blight, b. Pseiidomonas vitans, polar flagella 
stained with Casares-Gil's stain, c. gray mould rot; notice the 
numerous Botrytis fruiting heads on the wilted lettuce head. 



Lettuce Diseases 149 



This disease does not cause a rot of the leaves. The 
trouble is confined mainly to the edges of the foliage, 
marring the appearance and the market value of the 
product. The varieties most affected seem to be 
the Black-seeded Simpson, the Improved Hansen, 
and the Big Boston. Of the varieties less suscep- 
tible may be mentioned the Early Curled Simpson, 
and Vaughan's All Season. The variety Grand 
Rapids seems to be immune. 

The Organism, Pseudomonas niarginale is a 
short rod, rounded at both ends and motile by means 
of polar flagella. It forms capsules but no endo- 
spores, liquefies gelatin quickly and produces no gas. 

Control. Infected material should be destroyed' 
by fire. In watering, splashing should be avoided. 
Soil sterilization with steam or formaldehyde (see 
pp. 32-43) is recommended. 

Downy Mildew 

Caused by Bremia lactuca Reg. 

Symptoms, Affected leaves lose their natural 
green color and turn yellow. A careful examination 
will disclose a delicate downy web on the under side 
of the foliage which will have a wilted appearance. 
The downy web consists of the conidiophores of 
the fungus. These appear singly and are much 
branched. The conidia germinate by means of a 
germ tube. Downy mildew is a disease which is 
more troublesome in Europe than in the United 
States, and it is more serious on greenhouse lettuce 



150 Diseases of Greenhouse Crops 



than on that grown in the open. In the field it usu- 
ally attacks fall lettuce. Downy mildew attacks 
not only lettuce, but also chicory and numerous 
other Compositse. 

Control, This disease is controlled in the same 
way as lettuce drop (see p. 151). 

Gray Mold 

Caused by Sderotinia fuckeliana De Bary. 

Symptoms, Gray mold attacks grapes in Europe 
but in the United States it is commonly met with 
on lettuce plants which are fully developed and 
somewhat overgrown. The disease is manifested 
by soft, watersoaked spots on the foliage, causing a 
wilting. The spots soon become coated with the 
fruit of a gray mold. The fungus has two stages, 
the Botrytis cinera Pers. stage, which is commonly 
found as a gray mold on wilted lettuce leaves (fig. 
26, c); the other is the winter or apothecial stage, 
known as Sderotinia fuckeliana, American botanists 
have not as yet been able to connect these two forms. 
It seems, however, that Istvanffi was able to con- 
firm the work of De Bary, who first indicated the re- 
lationship of Botrytis cinerea with Sderotinia 
fuckeliana. 

Control^ see Lettuce Drop, p. 151. 

Lettuce Drop 

Caused by Sderotinia lihertiana Fckl. 
Symptoms. The term drop best describes the 

♦Istvanffi, G. De, Ann. de I'institut central ampel. roy. Hon- 
grois: 183-360, 1915. 




Fig. 27. Lettuce Diseases. 

a. Drop (after Humphrey), h. Septoria leaf spot, c. 
same as b. but older spots, d. pycnida, e. pycniospores (af- 
ter Selby). 



Lettuce Diseases 151 



symptoms of the disease. The first sign is a wilting 
of the lower leaves, which is immediately followed 
by a drooping of upper ones until the entire plant 
is involved. The affected plant has a sunken ap- 
pearance as if scalded with boiling water (fig. 27, 
a.). In examining a dead plant, a white cottony 
fungus growth is found on the under side of the 
lower leaves, and near the moist regions at the stem 
end. 

When the plants are fairly rotted, there appear 
on the cottony mycelial growth mentioned above, 
black bodies, or sclerotia, which vary in size from 
a pinhead to a grain of com. The three definite 
symptoms of the disease may be summarized: (1) 
drooping, (2) cottony-like mycelial growth on the 
under surface of the affected leaves, (3) the appear- 
ance of sclerotia. The latter help to csnry over the 
fungus during the winter. After the sclerotia have 
been in the soil over winter, they germinate in the 
following spring by sending out small mushroom-like 
fruiting bodies known as apothecia. The latter con- 
tain small sacs or asci which bear the spores. 

Control. Lettuce drop is favored by high tem- 
perature, overwatering, and poorly drained beds, 
leaky roofs, and insufficient ventilation. To check 
the disease a low night temperature of 50 degrees 
F. should be maintained. The water should also be 
withheld and an abundance of ventilation giren es- 
pecially during cloudy weather. Soil sterilization 
with steam or formaldehyde is also recommended. 



152 Diseases of Greenhouse Crops 



Leaf Spot 

Caused by Septoria lactuccz Pass, and Septoria 
consimilis E. and M. 

This disease is induced by two species of Septoria 
fungi. The symptoms produced by both are so near- 
ly alike that it is difficult to distinguish' one from • 
the other, except by microscopic examination. Pale 
brown discolored spots appear on the older leaves 
with numerous black pycnidia in the center (fig. 27, 
b-e.). The disease is of little economic importance, 
as it usually occurs late in the season, on plants which 
have nearly passed their usefulness. The Boston 
variety is considered resistant, while the Salamander 
and the Wonderful are more susceptible to leaf spot. 

Shot Hole 
Caused by Marsonia perforans E. and E. 

The disease is of little economic importance. Af- 
fected leaves are covered with dry spots which drop 
out, leaving irregular perforations. Along the bor- 
der of these holes, the causative fungus may be found 
abundantly fruiting. The disease attacks the mid- 
ribs of the leaves as well as the stem of the plants. 
It seems to be more prevalent under conditions of 
surface irrigation. 

With sub-irrigation, on the other hand, it is not 
found to cause any damage. 




Fig. 28. Lettuce Diseases. 

a. Lettuce rosette (to right diseased, and to the left healthy plant), b. 
Rhizoctonia ettect on roots; to right healthy roots, to left two diseased ones. 



Lettuce Diseases 153 



Cercospora Leaf Spot 

Caused by Cercospora lactuc(Z Stev. 

This disease is as yet of no importance in the 
United States. The causal fungus attacks the older 
and lower leaves forming numerous irregular spots. 

Rosette 

Caused by Rhizoctonia solani Kuhn. 

Symptoms. The disease attacks young seedlings 
by causing a damping off. Transplanted seedlings 
show infection at an early stage. Unlike healthy 
plants, they fail to send out new leaflets. The gen- 
eral growth takes the form of a rosette. The axis 
bearing leaf remains stunted. The roots show nu- 
merous deep lesions, and in an advanced stage are 
considerably rotted (fig. 28, b.). For a description 
of the causal organism, see p. 20, and for meth- 
ods of control see Lettuce Drop, p. 151. 

Root Knot, see Nematode, p. 28. 

Mint {Mentha sp,) 

Cultural Considerations. Mint is often forced on 
a small scale. The plants are easily grown, and re- 
quire about the same indoor conditions as the let- 
tuce. 

Diseases of the Mint 

Indoor mint may be subject to but one disease of 
importance. 



154 Diseases of Greenhouse Crops 



Rust 

Caused by Puccinia mentliiz Pers. 

This disease attacks about thirty-five members of 
the mint family. All the three stages of the fungus, 
i.e,^ secidiospores, uredospores, and teleutospores, oc- 
cur on the same host. The disease is characterized 
by brown sori which are at first cinnamon colored and 
later become chestnut brown. Diseased leaves curl 
and dry up. The infected parts of plants should be 
destroyed by fire. 

MusKMELON {Cucumis melo) 

Cultural Considerations, Muskmelon culture is 
little different from that of the cucumber (fig. 29.). 
However, the former is very sensitive to cold drafts 
and sudden changes in temperatures. For forcing, 
the heavier types of soil seem to be more desirable 
than the lighter ones. The fertilizer requirements 
for muskmelons are practically the same as those 
for cucumbers. Muskmelons require an abundance 
of soil moisture, but are sensitive to overwatering. 
It is also essential to maintain a high humidity in 
the house during the period of active growth. Dur- 
ing pollination and the ripening of the fruit the 
above condition is unnecessary. The temperature 
should be about 70 to 75 degrees F. at night and 
from 80 to 85 degrees Fahrenheit during the day. 
Muskmelons, like cucumber blossoms, must be pol- 
linated artificially, since both male and female flow- 



Fig. 29. 

Typical muskmelon house, showing method of trailing and supporting fruit. 



Muskmelon Diseases 155 



ers are distinct. The pollination is done by means 
of a camel's-hair brush, where the pollen from the 
male blossoms is rubbed on the stigma of the female 
flowers. 

Diseases of the Muskmelon 

Like cucumbers, greenhouse muskmelons are sub- 
ject to numerous diseases. 

Bacterial Wilt 

Caused by Bacillus tracheiphillus Ew. Sm. 

Symptoms, The symptoms of bacterial wilt are 
very striking. At first a few leaves of the plant are 
wilted. Soon after, the entire plant wilts and dies. 
Upon cutting through an infected stem, one observes 
a whitish viscid exudate that .oozes out from the 
vascular bundles of the cut surface. If one places 
his finger on the viscid substance and then gently 
removes it, the bacteria will be strung out into nu- 
merous delicate threads resembling cobwebs. The 
disease works quickly, and the change of leaf color 
from bright to dull green is also sudden. Musk- 
melons, unlike squash, show no tendency to recover 
temporarily from wilt. 

Bacterial wilt is spread about through the bites 
of leaf-eating beetles, such as striped cucumber 
beetle {Diabrotica vittatd). 

The Organism. B, trackeiphilus is a short 
straight rod with rounded ends. The organism oc- 
curs singly, in pairs, or rarely in chains of four; it is 



156 Diseases of Greenhouse Crops 



motile by means of flagella. It grows slowly on 
gelatine which is not liquefied. On potato cylinders 
growth is vigorous, resulting in a gray-white film 
with no changes manifested in the substratum. 
There is no gas production and the organism is 
aerobic. 

Control, Infection begins at a place of injury 
that has been produced by the bite or puncture of 
insects. Hence, any attempt to control wilt should 
first aim to control insect pests (see pp. 381-410). 

Downy Mildew, see Cucumber, p. 138. 

Powdery Mildew 

Caused by Erysiphe polygoni D. C. 

This disease is the same as the mildew which at- 
tacks cucumbers and numerous other hosts. Mildew 
is prevalent on greenhouse melons. It is character- 
ized by powdery white patches on the leaves. For 
control, see p. 323. 

MYC0SPHi5:RELLA WiLT 

Caused by Mycosphczrella citrullina (Sm.) Gr. 

Symptoms. This form of wilt is often a serious 
greenhouse trouble. Grossenbacher found that in- 
fection is localized at the nodes and not at the inter- 
nodes. The injury from Red Spider or from other 
sucking insects is perhaps responsible for opening 

♦Grossenbacher, J. G., New York (Geneva) Agr. Expt. Sta. 
Tech. Bui. 9: 197-229, 1909. 




1 

a 

Fig. 30. MusKMELON Diseases. 

a. Alternaria leaf spot, b. Alternaria spore (after Schwarze). 



Muskmelon Diseases 157 



the way to this disease. A characteristic of the 
trouble is that the edges of the infected areas are 
covered with an oily, green to raisin-colored gum. 
The older parts of the spots are either dark and 
gummy or gray and dry, bearing numerous brown 
pycnidia. 

The Organism. The perithecia are roundish, 
rough, dark brown to black, and almost superficial 
on the surface of the spots. The necks of the peri- 
thecia are hairy, the ascospores are cylindrical, two- 
celled, hyaline, and slightly constricted at the center. 

Control. Spraying with Bordeaux mixtures when 
the plants are about half grown and before the dis- 
ease appears is recommended. Spraying should be 
continued so that the growing parts are kept cov- 
ered with the fungicide. 

Anthracnose, see Cucumber, p. 141. 

Leaf Blight 

Caused by Alternaria brassica var. nigrescens 
Pegl. 

Symptoms. The disease begins as small round 
spots which gradually enlarge. These spots are dry, 
brown in color and made up of concentric rings or 
zones (fig. 30, a and b.). Usually the spots are very 
numerous and their presence causes the leaves to curl 
and dry up prematurely, leaving bare vines and un- 
protected fruit. As a result, the melons ripen early 
and have an insipid taste, and are very poor shippers. 
Leaf blight is most serious under field conditions. 



158 Diseases of Greenhouse Crops 



Control, The disease may be kept in check by- 
spraying with a weak solution of Bordeaux mix- 
ture. 

Southern Blight 

Caused by Sclerotium rolfsii Sacc. 

Southern blight, a disease that attacks a large va- 
riety of hosts, is a serious melon disease in the South- 
ern States. The injury in most cases is confined to 
the foot of the stem, the girdling and rotting of 
which finally causes the death of the affected plant. 
In the case of the cantaloupe, the fruit itself is at- 
tacked, infection usually taking place at a point 
where it touches the ground. The disease appears 
first as a slight soft spot which enlarges quickly, 
changing the entire mass of the fruit to a mushy 
pulp. The exterior of the affected melon is rapidly 
covered with a white cottony growth consisting of 
the mycelium of the fungus. Later there appear 
numerous whitish bodies known as sclerotia which 
turn yellowish and then brown. They help to carry 
the fungus over the winter. For methods of con- 
trol, see pp. 32-43. 

Root Knot, see Nematode, p. 28 (fig. 31). 



I 




Fig. 31. Root Knot of Muskmelon. 



CHAPTER 13 



THE MUSHROOM, AgaHcus campestris L, 

Cultural Considerations. As a rule florists are not 
as yet giving the mushroom the attention and con- 
sideration which it deserves. It is a crop which 
adapts itself particularly well to growth under 
benches, so that it utilizes all the extra greenhouse 
space (fig. 32, a and b.). Like all other remunera- 
tive crops, it requires skill to insure its permanent 
success. 

Temperature, Mushrooms may be grown in to- 
mato houses. In this case, the day temperature 
should run from 60° to 70° F. and the night tem- 
perature about 55° F. It should never be allowed 
to fall below 50 degrees. At less than 50° the crop 
does not thrive, although the spawn in the soil 
may endure freezing temperature without being 
killed. 

Preparation of Soil. In preparing the soil, fresh 
horse manure is mixed with loam as follows: To 
three shovelfuls of manure add one of loam, piled 
alternately in thin layers. This is kept for three 
days, but mixed every day in order to prevent the 
rapid fermentation or heating. This mixing is con- 
tinued until all danger of spontaneous combustion 

159 



i6o Diseases of Greenhouse Crops 



is over. At this stage, the manure loses its rank 
odor and is ready to be put in the bed. 

'Preparation of the Beds. The beds should be lo- 
cated preferably under the center benches, and in- 
closed in rough boards eight inches wide and one 
inch thick. The boards are set on edge and raised 
slightly above the floor so that with a bed ten inches 
thick the top of the bed would not extend much 
above the upper edge of the board. A layer of pre- 
pared manure is then spread evenly over the bot- 
tom of the bed, to the depth of three inches, and 
firmly pressed down by pounding with a brick. Two 
other layers of manure, each three inches thick and 
firmly pressed down are laid on the first, making 
the bottom about eight inches thick. A thermometer 
is placed in the manure and the temperature watched 
until it registers about 90 degrees F. 

spawning the Bed, When the temperature of 
the manure in the bed ceases to rise above 90 degrees, 
it is ready to be planted with the spawn. The lat- 
ter is usually bought in bricks, sixteen of which make 
a bushel. Each brick is broken into twelve equal 
parts, which are inserted about an inch deep in 
the manure bed with intervals of nine inches. The 
manure is then packed firmly over the pieces, leav- 
ing the surface of the bed smooth again. Two 
weeks after planting the spawn, the beds are coated 
with two inches of the mellow loam prepared as 
stated above. The loam should be neither dry nor 
wet, but simply moist. It should not be applied 
until it is certain that the spawn has commenced 



Mushroom Diseases i6i 



growing. This becomes noticeable as a bluish-white, 
moldy growth. The loam beds should be covered 
with a three-inch layer of excelsior to keep them 
from drying. The mushroom beds should be pro- 
tected from the drippings of the overhead benches 
by a roof of heavy waterproof cover. 

Watering. Care should be taken never to over- 
water the beds. It is necessary to apply enough 
water to keep the surface of the bed moist, but not 
soaked. In watering the excelsior is often rolled 
back or else water may be applied on top of it. 
Beach''' recommends as the beds begin to bear that 
they be watered twice a week with nitrate of soda 
dissolved at the rate of one ounce to each gallon of 
water. It is applied with a watering can in a quan- 
tity sufficient to moisten, but not to soak the beds. 
To promote good bearing and to prevent a rapid ex- 
haustion, the beds are often coated over again with 
a layer one and a half inches thick of fine mellow 
loam. 

Diseases of the Mushroom 

Mushrooms are subject to few diseases. There 
are but two which need concern the greenhouse man. 

Bacterial Spot 

Caused by Pseudomonas fluorescens (Fl.) Mig. 
This disease, although serious, seems to be re- 

* Beach, S. A., New York (Geneva) Agr. Expt. Sta. Fourteenth 
Ann. Rept: 33i-34i> 1895. 



i62 Diseases of Greenhouse Crops 



stricted as yet to the mushroom caves in St. Paul, 
Minnesota. The trouble was first described by 
Tolaas."^ 

Symptoms, It is characterized by an unsightly 
spotting of the caps, the severity of which differs 
in the cultivated varieties, especially the large white 
kinds. The spots, which do not extend deep into 
the flesh, appear while the mushroom is in the but- 
ton stage, or when the cap is fully expanded. The 
spots are at first pale yellow, but later become a 
chocolate brown. Though the disease does not seem 
to reduce the yield, the market value of the spotted 
mushrooms is considerably reduced. 

The Organism, Fseudomonas fluorescens is a 
small rod rounded at both ends and motile by means 
of polar flagella. It is a facultative anaerobe ; pro- 
duces no endospores, no gas, but liquefies gelatine. 
On beef and potato agar, it produces a shiny gray- 
ish white growth accompanied by a greenish pigmen- 
tation, which diffuses in the substratum. 

Control, Spraying the mushroom caps with solu- 
tions of benetol, sodium carbonate, or copper sul- 
phate seems to have no beneficial effect. On the 
other hand, fumigating the beds with sulphur before 
planting the spawn insures the production later of a 
clean crop of mushrooms. The amount of sulphur 
to use is about one and a half pounds to each thou- 
sand cubic feet of house space. 

*Tolaas, A. S., Phytopath. 5: 51-53, 1915. 



Mushroom Diseases 163 



The Mycogone Disease 

Caused by Mycogone perniciosa Mag. 

The Mycogone is a very destructive mushroom 
disease. The exact amount of its distribution in the 
United States is as yet unknown. However, if 
once introduced in a house, it is likely to ruin the en- 
tire crop. 

Symptoms, The symptoms of the disease are 
often various. The presence of the malady may be 
indicated by small tubercules on the cap and by a 
form of fluffy white growth on the gills, which in- 
terferes with their normal development. The result 
is distorted caps and stipes, and finally, a general 
darkening and decay of the tissue. In severe cases, 
monstrous soft masses with thick white fungus coat- 
ings are observed in houses in which the disease is 
very prevalent. In this case, the affected plants 
have little resemblance to mushrooms. They decay 
rapidly, and emit a very disagreeable odor. 

The Organism. The spores of Mycogone perni- 
ciosa are very characteristic. They consist of two 
cells, the upper spherical, rough, and covered with 
warts, the lower hyaline and smooth. Both cells 
possess thick walls. 

Control, According to Veihmeyer,* there are no 
evidences that tend to show that the Mycogone dis- 
ease is carried with the spawn manufactured by the 
"tissue culture" method. It is very probable, how- 
ever, that the disease was introduced into this coun- 

♦Veihraeyer, F. J., U. S. Dept. of Agr. Bui. 127: 1-24, 1914. 



164 Diseases of Greenhouse Crops 



try from France with imported virgin spawn col- 
lected at random from fields. The disease may be 
introduced into a new place with the manure and 
then spread quickly in a number of ways. Immedi- 
ate precautionary measures are essential for the con- 
trol of this trouble. Diseased plants when first no- 
ticed should be pulled out and burnt. Allowing these 
infected plants to decay in the beds is a sure means 
of spreading the fungus broadcast. The gain from 
keeping the beds free from diseased specimens will 
more than compensate for the trouble. At the end 
of the season the soil in beds should be carried away 
to a distance where mushrooms will not be grown, al- 
though it may be used for garden purposes, since 
the Mycogone disease is known to attack only mush- 
rooms. After the house has been thoroughly cleaned 
out, it should be disinfected with the formaldehyde 
gas method. This is carried out as follows: For 
every thousand cubic feet of house space use three 
pints of formaldehyde and twenty-three ounces of 
potassium permanganate. The potassium perman- 
ganate is placed in two or three earthen or wooden 
vessels, each having a capacity of one quart to every 
ounce of permanganate. When ready for the opera- 
tion, the mushroom house is sprinkled with water, 
the potassium permanganate placed in the recepta- 
cles, the formaldehyde is poured evenly over the 
permanganate, and the greenhouse doors are closed at 
once. They are kept closed for twenty-four hours 
and then opened to allow the formaldehyde fumes to 
escape. All lights must be kept away from the house 



Mushroom Diseases 165 



while they are being fumigated since formaldehyde 
gas explodes upon coming in contact with fire. Mush- 
room houses thus treated may be thoroughly rid of 
the Mycogone disease, but care must be taken to 
prevent reinfection. 

It is hardly necessary to add that all tools and 
wagons which were used in connection with the in- 
fected houses should be disinfected before being used 
again. All such tools and vehicles should be washed 
in a solution of one pint of formaldehyde in twenty 
gallons of water. Throughout the process the oper- 
ator must exercise extreme care not to inhale any of 
the poisonous formaldehyde fumes. 



CHAPTER 14 



PARSLEY {Carum petroselinunCj 

Cultural Considerations, Parsley is easily forced 
and requires no particular care. Any of the curly- 
leaved varieties lend themselves to forcing. 

Diseases of Parsley 

Under greenhouse conditions parsley is subject to 
but few diseases. 

Drop, see Lettuce, p. 150. 
Late Blight, see Celery, p. 130. 

Pea {Pisum sativum) 

Cultural Considerations, Peas are seldom forced, 
although they could be easily grown in the green- 
house. No attempt should be made to grow them 
after March. They require a night temperature of 
40 to 50 degrees F. and a day temperature of about 
60 degrees. They are readily injured by higher tem- 
peratures. They thrive best in solid beds and re- 
quire an abundance of water and good drainage. 
The early dwarf varieties lend themselves well to 
forcing. 

166 



Fig. 33. ScLEROTiNiA Rot on Pea Pods. 



Pea Diseases 



167 



Diseases of the Pea 

Indoor peas may become subject to several dis- 
eases. 

SCLEROTINIA TOt (fig. 33), SCC LeTTUCE dlOp, p. 

150. 

Thielavia Root Rot 

Caused by Thielavia hasicola Zopf. 

Symptoms, Plants severely infected with Thiela- 
via have practically no root system, for the latter is 
destroyed by the fungus as rapidly as they are 
formed. All that is left is a charred, blackened stub. 
The diseased host constantly attempts to produce 
new roots above the injured part, but these in turn 
become infected. Such plants linger for a long time, 
but fail to set pods which are of any value. 

The Organism, The mycelium of Thielavia hasi- 
cola is hyaline, septate, and branched. The Myce- 
lium becomes somewhat gray with age. Three kinds 
of spore forms are produced — endospores, chlamy- 
dospores, and ascospores. The endospores are so 
called because they are formed inside a special thread 
of the mycelium. This is the spore form that com- 
monly occurs in pure cultures of artificial media 
and on the host. The endospore case is fonned on 
terminal branches with a somewhat swollen base 
and a long tapering cell. The endospores are formed 
in the apex of this terminal cell and are pushed out 
of the ruptured end by the growth of the unfrag- 



i68 Diseases of Greenhouse Crops 



merited protoplasm of the base. They are hyaline, 
thin walled, and vary from oblong to linear in shape. 
The chlamydospores are thick walled, dark brown 
bodies borne on the same mycelium as the endo- 
spores. This type of spore is formed in great abun- 
dance on the host and particularly within the af- 
fected tissue. The ascospores are lenticular in shape 
and are borne in asci or sacs within black perithecia. 
This stage, however, has not been found on the pea 
nor in pure culture. 

Control, Since the causal organism is introduced 
with infected manure or soil, sterilizing the beds 
with steam or formaldehyde (see pp. 32-43) is 
recommended. 

Powdery Mildew, see Bean, p. 111. 

Pod Spot 

Caused by Spharella pinodes (Berk, and Bl.)^ 
Niessl. 

Symptoms, On the stem the trouble appears as 
numerous elongated lesions. These spread to such 
an extent as actually to girdle the affected stem. On 
the leaves are formed oval spots, grayish in the cen- 
ter, and limited by a dark band. The pods, too, 
become badly attacked and the symptoms there re- 
semble those on the stems. The disease works its 
way from the pods to the seed within. 

The Organism, The causative fungus has two 
spore stages. The pycnidia bear the hyaline, two- 
celled spores, and are formed within the dead tissue 



Pepper Diseases 



of the affected stems, leaves, or pods. The pycni- 
dial stage is known as Ascochyta pisi Lib. The win- 
ter or ascospore stage has only recently been discov-^ 
ered by Stone, who found it on pods and stems 
previously affected, and on culture media. The fun- 
gus may be carried from year to year as dormant 
mycelium within the seed, or in the ascospore stage. 

Control. Seed treatment will not be of any value 
since the fungus is hidden within the seed. No out- 
side treatment is capable of reaching the parasite 
within. Seed should be secured from localities 
known to be free from the disease. Susceptible 
varieties, such as French June, Market Garden, 
American Wonder, should be discarded. The Alaska 
variety is said to be more resistant. 

Pepper (^Capsicum annum). 

Cultural Considerations, Peppers are not diffi- 
cult to force, although they are not extensively 
grown on a commercial scale in the greenhouse. 
Peppers thrive best at a temperature slightly lower 
than that required by cucumbers (see p. 133). The 
Sweet Mountain variety seems to lend itself best 
to forcing. 

Diseases of the Pepper 

The pepper plant is considered comparatively 
hardy, and its few diseases usually become trouble- 
some only when the crop is neglected. 

Sun Burn (fig. 34, d), see p. 94. 
♦Stone, R. E., Annales Mycol., lo: 564-593, 1912. 



170 Diseases of Greenhouse Crops 



Anthracnose 

Caused by Glomerella piper ata (E. and E.) S. 

Anthracnose is a serious disease which is usually 
confined to the fruit. Its symptoms are character- 
ized by round, soft, sunken, pale spots (fig. 34, 
a). The summer or conidial stage is known as 
Gleosporium piperatum E. and E. and is found as 
salmon colored pustules abundantly scattered over 
the spots. The ascospore stage may develop in pure 
cultures of the fungus. 

Black Anthracnose 

Caused by Collet otrichum nigrum E. and H. 

This form of anthracnose differs from the disease 
described above only in that the spots turn jet black. 
The trouble attacks the young as well as the mature 
fruit. The winter or ascospore stage of the causa- 
tive fungus has not as yet been found. It is very 
probable that the fungus (fig. 34, b-c) is carried 
over as viable mycelium on the infected fruit left 
over in the field. Both forms of anthracnose may 
be controlled by spraying with Bordeaux mixture. 

Fruit Spot 

Caused by Macrosporium sp. 

This disease, which is as important as anthracnose, 
attacks the fruit at the blossom end. The peppers 
that are attacked are half rotted, black, and moldy. 



Pepper Diseases 



171 



Little is known about the causative fungus. It is 
probable that the disease has the same origin as 
the blossom end rot of tomatoes, and that the Macro- 
sporium fungus is only secondary. Spraying with 
Bordeaux mixture is recommended. 

Leaf Spot 

Caused by Cercospora capsisi H. and W. 

This disease is characterized by roundish raised 
spots on the upper surface, at first brown, later be- 
coming gray brown. They are limited by a dark 
zone, beyond which the leaf tissue is pale and chlor- 
otic. Where the spots are abundant the leaves turn 
yellow, wilt, and fall off prematurely. 

The conidiophores of the fungus are formed in 
clusters on both surfaces of the spots. The conidia 
are dilutely brown, clavate, and several septate. As 
a control measure spraying with Bordeaux mixture 
is recommended. 

Southern Blight 

Caused by Sclerotium rolfsii Sacc. 

Symptoms, Affected plants show a drooping of 
the young leaves at the tips of the branches. At 
night the plant seems to recover and it appears nor- 
mal the next morning. This recovery, however, is 
only temporary. Wilting generally follows, and 
after three or four days the leaves become completely 
yellow, wilt, droop, and die. In another day, the 



172 Diseases of Greenhouse Crops 



stem of the plant loses its green color, dries up, and 
dies. On pulling out a plant freshly wilted, we 
find a shrunken discolored area at the foot of the 
stem, slightly below ground level. In more ad- 
vanced stages, the shrunken area is covered by a 
delicate web of white mycelial threads, and after the 
death of the plant numerous brown mustardlike 
sclerotia are found on the surface of the affected 
tissue. 

Control, The causal fungus is introduced in the 
greenhouse with infected soil or manure. Soil ster- 
ilization with steam or formaldehyde (see pp. 32- 
43) is recommended. 



CHAPTER 15 



RADISH {Raphnus sativus) 

Cultural Considerations, There are few green- 
houses near a large city which do not force radishes. 
The radish more than any other plant thrives best 
in full light. Shade favors the development of 
foliage over root. The varieties best liked by the 
market are those of the Scarlet Rose type. A light 
sandy soil which contains sufficient humus is ideal 
for forced radishes. Radishes need plenty of water. 
However, overwatering may favor damping off. The 
most favorable temperatures are 43 to 45 degrees 
F. at night and about 55 to 62 degrees during the 
day. In warm days the ventilators should be fully 
open. On cold days they may be opened a little at 
a time. Radishes are often intercropped with let- 
tuce or cauliflower. 

Diseases of the Radish 

Radish is subject to many diseases in common 
with the cauliflower and numerous other crucifers. 
Club Root, see Cauliflower, p. 122. 

Black Rot 

Caused by Fseudomonas campestris (Pam.) 
Ew. Sm. 

173 



174 Diseases of Greenhouse Crops 



Symptoms, Black rot on radish is confined mostly 
to the tender white-rooted varieties, especially the 
Icicle. The black-rot germ penetrates the lateral 
feeding rootlets, from which it works its way into 
the main root. In cutting across a diseased radish, 
its interior fibrovascular bundles are found to be 
blackened. Such radishes are useless for the mar- 
ket. The disease seldom attacks the red or the 
black-skinned varieties. For further consideration 
see Black Rot, p. 124. 

Scab 

Caused by Actinomyces chromo genus Gasp. 

Scab is not a common field disease of radishes. 
It is, however, found to be troublesome on the crop 
grown in greenhouses. The French Breakfast va- 
riety is commonly susceptible to the disease. The 
trouble may be expected if the crop is planted in a 
soil which previously produced a potato crop that 
was badly scabbed or where infected manure was 
used, or too much lime applied. For methods of 
control, soil sterilization with steam or formalde- 
hyde is recommended (see pp. 32-43). 

Damping Off 

Caused by Rheo sporangium asphanidermatum Ed. 

Symptoms, The disease seldom attacks the leaves. 
The injury is confined to the roots only. Diseased 
plants are flabby, pale or yellowish, with a tendency 
to wilt. The roots when pulled out will show that 



Fig. 35. Rheo SPORANGIUM Rot of 
Radish. 



Radish Diseases 



175 



the rootlets have been rotted off and that the main 
root, too, has rotted at various intervals * (fig. 35). 

Control, This disease may be controlled in the 
same way as damping off (see pp. 32-43). 

Downy Mildew, see Cauliflower, p. 127. 

Damping Off, see Rhizoctonia, p. 20. 

Root Knot, see Nematode, p. 28. 

Rhubarb 

Cultural Considerations, Rhubarb is a popular 
greenhouse crop, and is extensively forced for win- 
ter use. Greenhouse rhubarb is superior in quality 
and in texture to the out-of-doors variety. The 
plant may grow in total darkness, but a diffused 
dim light is advisable. The roots before being 
planted should be thoroughly frozen for a few days, 
then given a short rest. In the milder climates of 
the South, the roots should be dried before planting. 
Both of these treatments will accelerate growth. 
When well established the plants need not be 
watered more than twice a week. The temperature 
for rapid growth ranges from 50 to 55 or 60 degrees 
F. Under lower temperatures, the plants will re- 
quire a longer time to mature. The varieties which 
lend themselves well to forcing are the Paragon, 
Mammoth, Linnseus, Strawberry, and Victoria. 

*A description of the causal organism is given in the author's 
previous volume, "Diseases of Truck Crops and their Control," 
p. 210, 1918. (E. P. Dutton & Co., New York.) 



176 Diseases of Greenhouse Crops 



Diseases of the Rhubarb 

The Rhubarb is considered a very hardy plant. It 
is subject to but few diseases. 

Powdery Mildew 

Caused by Peronospora jaapiana Mag. 

This disease is fairly prevalent in Europe. Its 
presence in the United States is not definitely known. 
At any rate it is of little economic importance. 

Rust 

Caused by Puccinia phragmitis Schum. 

Rust is a disease of little consequence. The 
secium known as Mcidium ruhellum occurs on the 
rhubarb. The uredinia and the telia are found on 
Phragmitis. By destroying the Phragmitis the rhu- 
barb rust will be prevented. 

Anthracnose 

Caused by V ermicularia polygoni-virginica Schw. 

This disease is frequently found on old leaves 
of rhubarb grown out of doors. It is of little eco- 
nomic importance. 

Leaf Spot 

Caused by Ascochyta rhei E. and E. 

Like anthracnose, this trouble is of little impor- 



Spinach Diseases 177 



tance to greenhouse rhubarb. The causal fungus 
causes irregular spots, which fall out and give the 
affected foliage a ragged appearance. 

Spinach {Spinacia oleracea) 

Cultural Considerations. There has developed 
lately a tendency to grow indoor spinach on a large 
scale. Growers who have tried it out find that it is 
as profitable a crop as lettuce. The cultural re- 
quirements of spinach are the same as those of let- 
tuce, see p. 145. If the soil is deficient in nitrogen an 
application of nitrate of soda will be very beneficial. 
The aim should be to encourage rapid growth, which, 
moreover, insures high quality. Vigorous broad- 
leaved varieties such as Victoria, New Zealand, and 
others are recommended. 

Diseases of the Spinach 

Indoor spinach is generally subject to less diseases 
than that grown out of doors. 

Malnutrition 

Cause : An excess of acidity or a lack of soil humus. 

Symptoms, Malnutrition may be met with where 
commercial fertilizers are used to the exclusion of 
organic manures. The margins of the veins of the 
leaves become yellow while the central part takes 
on a mottled appearance. The outer leaves are usu- 



178 Diseases of Greenhouse Crops 



ally the first to suffer; soon, however, the entire 
plant exhibits similar symptoms and ceases to grow. 

ControL Where this disease is prevalent, the 
soil should be changed, or sufficient organic matter 
in the form of well rotted m.anure incorporated in 
the beds. Malnutrition as a rule is not prevalent 
in the greenhouse, for it is rare that a greenhouse soil 
is lacking in humus. 

Downy Mildew 

Caused by Peronospora effusa Rabenh. 

Symptoms, The trouble is characterized by yel- 
low spots of conspicuous size on the upper part of 
the leaves. On the under side of the leaves, and 
corresponding to the spots above, is seen a mat com* 
posed of the dirty white or violet gray fruiting 
bodies of the fungus. The disease is often prev- 
alent in the field. 

The Organism, Downy mildew is caused by the 
fungus Peronospora effusa. The spores of the para- 
site are borne on branches, which generally emerge 
through the breathing pores or stomata of the lower 
part of the leaf and germinate by sending out a 
slender germ tube. Infection takes place when the 
germ tube penetrates the upper side of the leaf, gen- 
erally through the stomata. The winter stage or 
oospores may be found in the affected leaves. 

Control, All infected material should be de- 
stroyed. Water should be withheld, and plenty 



Spinach Diseases 179 



of ventilation allowed whenever possible. The 
plants may be sprayed with a standard fungicide. 

Anthracnose 

Caused by Colletotrichum spinacia Ell. and Hals. 

Symptoms. It appears as minute, round, water- 
soaked spots on the leaves. These quickly enlarge 
and become gray and dry. In the spots will be 
found evenly-scattered, minute, dark tufts; these 
are merely fruiting pustules which also contain mi- 
nute black bristles or setae. The disease is not limited 
to any particular part of the plant. Infection may 
take place anywhere on the foliage, stems, or peti- 
oles. The spore pustules may be formed on the 
upper as well as on the lower surface of the leaf. 
Under moist conditions, the pustules take on a sal- 
mon tinge, indicating that there is an abundance of 
spores formed at that time. The spores may be 
carried from leaf to leaf and from plant to plant 
by insects, wind, or rain water. In badly infected 
beds, picking should not be done when the leaves are 
wet. Infected material should be destroyed by fire. 

The fungi Entyloma elUssii Hals, Fhyllosticta 
chenopodii Sacc, Cladosporium macrocarpum Preuss, 
and Heterosporium variahile Cke. do not seem to 
trouble indoor spinach but are rather serious out of 
doors. 



CHAPTER 16 



TOMATO {Lycopersicum esculentum) 

Cultural Considerations. The tomato is one of 
the three most important greenhouse vegetables. It 
is perhaps more difficult to grow than either lettuce 
or cucumbers. Great skill is required in the heating, 
watering, ventilating, and pollinating. To overlook 
any of these factors may result in failure. Of the 
numerous varieties which lend themselves to forcing 
the following are the most preferred by the Ameri- 
can and English growers: 

American Varieties English Varieties 

Beauty Best of All 

Bonny Best Carter's Sunrise 

Earliana Comet 
Magnus Frogmare 
Stone Globe 

Lorillard 
Peerless 
Sterling Castle. 

The tomato thrives best in a medium heavy loam. 
The plants are heavy feeders. The fertilizer must 
be well balanced mixtures. The nitrogen, for in- 
stance, should not take the place of the potash or 

180 



Tomato Diseases i8i 



the phosphoric acid. Tomato plants require a lib- 
eral supply of water. However, overwatering will 
encourage numerous diseases. On bright, sunny- 
days there is little danger of overwatering, but great 
care is required not to overwater during cloudy 
weather. 

The temperature for greenhouse tomatoes is very 
important. At night and on cloudy days it should 
be maintained at about 60 degrees F. During 
bright, sunny days higher temperatures will not be 
harmful. The house should be given all the ven- 
tilation possible. Even during cold days, the ven- 
tilators should be opened slightly at frequent in- 
tervals while a close watch should be kept on the 
indoor thermometer. 

Diseases of Tomatoes 

Greenhouse tomatoes are subject to a large num- 
ber of diseases. Many of these are of economic 
importance. 

Hollow Stem 
Cause, physiological. 

Symptoms. Hollow stem is a trouble manifested 
by seedlings in the bed, or after transplanting. The 
central portion of the head of the plant remains 
green while the lower leaves turn yellow. In se- 
vere cases, affected plants fall over as in damping 
off, with the absence, however, of signs of rotting. 



i82 Diseases of Greenhouse Crops 



Such plants when examined are found to have hol- 
low stems and seem too weak to stand up. 

Cause. There are several causes, any one or all 
of which may lead up to hollow stem. ( i ) A highly 
nitrogenous fertilizer applied to the seed bed to force 
the seedlings. (2) An abundance of water supply 
to make the fertilizer quickly available. (3) Sow- 
ing seeds of a rapid growing variety. (4) Trans- 
planting without hardening off. (5) Transplanting 
into a dry soil. 

Control, It is evident from what has been said 
that the fertilizer in the seed bed should be well 
balanced. Care should be taken to prevent the seed- 
lings from becoming leggy, and to see that they are 
properly hardened before transplanting. The Stone 
and its related varieties seem to be more resistant 
to hollow stem. On the other hand, the Dwarf 
Champion seems to be especially susceptible to hol- 
low stem. 

Winter Blight 
Cause, unknown. 

Symptoms, This disease seems to be very preva- 
lent on forced tomatoes in the United States and 
Canada. Howitt and Stone,"^ who have recently 
studied this disease, describe it as follows: The 
leaves show distinct brown or blackened, angular, 
diamond-shaped spots scattered between the larger 
veins. When the spots are numerous and close to- 
gether they appear as a distinct pattern. In a more 

♦Howitt, J. E., and Stone, R. E., Phytopath. 6: 161-166, 1916, 



Tomato Diseases 183 



advanced stage, the primary and secondary veins 
also become browned. Affected stems are peppered 
with minute brown lesions, irregularly scattered, and 
apparently superficially seated. In advanced stages, 
however, the lesions seem to work deeply into the 
vascular bundles. On the fruit the disease appears 
as surface lesions which are variously shaped. The 
surface of the spot may be unbroken and smooth, 
or rough and scabby. In advanced stages, the super- 
ficial lesions work in deeply in the flesh of the fruit. 
Upon maturing, the affected areas fail to take on 
the normal color. Such fruit is spotted and scabby, 
and is worthless for market purposes. Up to the 
present, the exact cause of the disease and methods of 
control are unknown. It seems that the trouble is 
not caused by a pathogenic organism, but rather by 
some unknown chemical or physical derangement of 
the soil. 

Blossom End Rot 
Cause unknown. 

Blossom end rot, also known as point end rot, 
may be found wherever tomatoes are grown. It is 
a disease of the fruit only. In some seasons fifty 
per cent or more of the fruit crop is ruined by it. 
It seems to be serious in dry weather and on light 
soils. 

Symptoms, Infection is manifested as a water- 
soaked spot at the blossom end of the fruit (fig. 
36, a.). The size of the spot may be that of a pin- 
head, or it may spread so rapidly as to involve half 



184 Diseases of Greenhouse Crops 



of the tomato. A few days later, the water-soaked 
spot becomes black and leathery and ceases to make 
further progress. Complete rotting of the fruit may 
be brought about by secondary invasions. 

Plants subject to frequent slight wilting produce 
a greater number of defective fruits. There seems 
no doubt but that the water supply in the soil is an 
important factor in limiting or increasing blossom 
end rot. The factors of drainage and cultivation 
are, therefore, important considerations. Although 
dry soils and drought favor the increase of the dis- 
ease, the state of health of the plant itself seems 
equally important. 

The use of fertilizers, too, seems to influence the 
trouble. Heavy applications of manure or of pot- 
ash seem to increase the rot, as do fertilizers in the 
form of ammonium compounds. This is especially 
true on sandy loams. On the other hand, nitrate 
of soda or lime acts as a check. In controlling blos- 
som end rot, the moisture of the air in the green- 
house seems also an important factor. On bright, 
sunny days, it is not advisable to keep the air dry. 
However, care should be taken not to keep the air 
of the house dry during the night, as this encourages 
numerous fungous diseases. 

Sunburn 

Tomatoes are often burned while they are on the 
vines by strong sunlight beating on the exposed fruit. 
This results in a scalding of certain parts, loss of 



Tomato Diseases 185 



color, and a local drying which produces white spots 
with a dry, peppery appearance. Such fruit is unfit 
for the market. 

Control. In houses where sunburn is prevalent it 
is advisable to have the house shaded and to plant 
varieties that have a dense foliage. 

Mosaic 

Cause unknown. 

A lengthy discussion on mosaic has already been 
given on p. 102. Mosaic on tomato is a common field 
and greenhouse trouble, conspicuous on stalks, fruit, 
and leaves. On the leaves it is manifested as a 
mottling of yellow areas on the tissue that causes 
the leaves to warp and grow unevenly. In severe 
cases the normal leaflets are replaced by a filiform or 
fern-like structure, with a striking dissected form. 
The blossom of the diseased plant usually drops off, 
and the few fruits that are set are small and de- 
formed. 

Southern Wilt 

Caused by Fseudomonas solanacearum Ew. Sm. 

Symptoms. Infected plants usually wilt rapidly 
without losing their green color. In large leaves, 
the main axis is bent downward in a drooping way. 
With the young plants the stems and foliage also 
droop and shrivel. The vascular system of such 
plants is browned, indicating the presence of the 
causative organism within. Upon cutting across a 
freshly wilted stem, one observes that a dirty white 



i86 Diseases of Greenhouse Crops 



to brownish white slime that is not sticky oozes out. 
In soft and rapidly growing plants, the whole pith 
is often converted into a watery slime. In toma- 
toes and eggplants the disease seldom attacks the 
fruit but is confined to the vegetative parts. 

Southern wilt attacks not only the tomato and 
eggplant, but it also causes a serious disease on po- 
tato, tobacco, peanut, nasturtium, ragweed, impa- 
tience, and verbena, in the open. 

The Organism. Fseudomonas solanacearutn is a 
medium-sized rod, with rounded ends and motile 
by means of polar flagella. Pseudo-zoogloese are 
common in old cultures. No spores are formed; on 
agar-agar, colonies are white, then dirty white, after- 
wards becoming brown with age. The organism 
does not liquefy gelatine and produces no gas. 

Control. All diseased plants should be carefully 
pulled out and destroyed by fire. The house should 
be given all the ventilation possible and water with- 
held for a while. Syringing of the plants should 
cease until the disease subsides. In watering care 
should be taken not to splash soil particles on the 
plant. All insect pests whether sucking or biting 
should be controlled, as these usually help to spread 
the disease. This trouble is likely to be prevalent 
in greenhouses in the Southern states. 

Damping Off. See Pythium. 

Late Blight 

Caused by Phytophthora infestans (Mont.) 
De By. 



Tomato Diseases 187 



Late blight is a disease of frequent occurrence on 
greenhouse tomatoes. 

Symptoms, Affected plants appear as though 
killed by frost. The disease first shows itself as 
small blackened areas on the leaves, stems, and 
fruits. These rapidly increase in size and cause the 
premature death of the affected host. Fruits which 
may not show signs of disease will develop the 
trouble in transit if coming from infected houses. 

The Organism. The mycelium of the fungus is 
hyaline, non-septate. As shown by Melhus* and 
others, the mycelium may be carried from year to 
year within the infected tubers. In fact this is but 
one way by which late blight is distributed. 
Through the stomata of the infected leaf emerge the 
slender conidiophores bearing the ovoid conidia. 
According to Melhus the conidia of Phytophthora 
infestans may germinate either directly by a germ 
tube or by the production of zoospores as in Pythium. 
The best germination occurs at the optimum tem- 
perature, which lies between lo and 13 degrees C. 
(50-57 degrees F.). The conidia may be killed by 
exposure for six to twenty-four hours to dry atmos- 
pheric conditions such as exist in an ordinary room. 
Frost which kills the top of the plants will also kill 
the conidia of Phytophthora. Light does not hinder 
germination and therefore has no inhibiting effect 
on infection. Investigation fails to show that Fhy- 
tophthora infestans produces sexual spores or 00- 

* Melhus, I. E., U. S. Dept. of Agr. Jour. Agr. Research, 5 : 59-65, 
1915. 



i88 Diseases of Greenhouse Crops 



spores within the affected tissue of the leaf or tuber. 
However, Clinton succeeded in developing what ap- 
peared to be oospores of the fungus in pure culture 
on oat agar. The oogonia appear as swollen terminal 
heads, cut off from the main thread by a cross wall. 
The antheridium resembles that of P. phaseoU. Ma- 
ture oospores have a medium thick, smooth, hyaline 
wall. How the oospores germinate is unknown. 

ControL Late blight of tomatoes may be con- 
trolled by spraying. The best results are obtained 
by using 5-5-50 Bordeaux. 

Buckeye Rot 

Caused by Phytophthora t err e stria Sherb. 

Buckeye rot is a disease which attacks the fruit. 
The trouble seems to be new and has been recently 
described by Sherbakoff.* So far as is known, the 
disease has appeared only in Florida. 

Symptoms. The disease, as the name indicates, 
appears as pale to dark greenish-brown zonate spots 
on the fruit. The rot is hard and somewhat dry 
when the fruit is green, but becomes softer as the 
tomato ripens. It usually begins at a point where 
the fruit touches the ground, which is most com- 
monly at the blossom end, and might be mistaken 
for blossom end rot were it not for the characteristic 
zonations. 

The Organism, The mycelium is at first continu- 
ous, then septate. Conidia germinate by means of 

♦Sherbakoff, C. D., Phytopath, 7:119-129, 1917. 



Tomato Diseases 189 



swarm spores. Chlamydospores are common, oospores 
frequent on cornmeal agar. Besides tomato fruit, P. 
terrestria causes a foot rot of citrus trees and a stem 
rot of lupines. 

Control, Fruit destined for distant markets 
should not be packed as soon as it is brought in from 
the house. If possible it should be kept a few days 
to allow for possible rot to develop so that the af- 
fected ones may be culled out and destroyed. Spray- 
ing with Bordeaux mixture is also recommended. 

Leaf Spot 

Caused by Ascochyta lycopersici Brun. 

This disease is of common occurrence but of lit- 
tle economic importance. It produces brown circu- 
lar spots which enlarge and change to grayish brown 
in color. 

Fruit Rot 

Caused by Fhoma destructiva Plowr. 

Symptoms. On the fruit the disease is character- 
ized by conspicuous dark spots on the side and at 
the stem end of both green and mature fruit. On 
the surface of the largest spots, numerous dark 
pycnidia may be seen. Besides attacking the fruit, 
the disease may also infect the foliage, causing dark 
spots which resemble those on the fruit. Affected 
leaves shrivel, droop, and sometimes drop off. The 
disease seems to be unable to attack potatoes or 
peppers. 



190 Diseases of Greenhouse Crops 

The Organism. The mycelium forms a dense net- 
work of fungal threads within the host tissue. The 
pycnidia are subglobose, carbonaceous, smooth, 
slightly papillate, and with a distinct central pore. 
The pycnidia are scattered and few. 

Leaf Spot 

Caused by Septoria lycopersici Speg. 

Symptoms, The first indications of the disease 
are minute water-soaked spots on the underside of 
the leaves. With time, these increase in size and 
become circular in outline v/ith a definite margin. 
The spots become hard, dry, dark, and shrunken, 
and when numerous they coalesce into large blotches, 
involving the entire leaflets and leaves; the latter 
soon droop, dry, and cling to the stalk, until broken 
off by the wind or by any other jar. Within the 
spots are formed minute black, glistening pycnidia 
while the spores exude yellowish mucilaginous drops. 

On the stems, the spots are similar to those on 
the leaves, although they are not so clearly defined, 
nor do they work in deep enough to form cankers. 
Spots may also occur on the calyx and on the fruit. 
The disease, however, is usually a foliage trouble. 
Of the more resistant varieties may be mentioned 
Mikado, King Humbert, Wonder of the Market, 
and Up to Date. Of the medium resistant varieties 
may be mentioned Alice Roosevelt, President Gar- 
field, Prelude, Ponderosa, and Magnum Bonum. 



Tomato Diseases 



191 



The Trophy and Ficarazzi are very susceptible 
varieties. 

The Organism. The mycelium of Septoria lyco- 
fersici is hyaline and septate. The pycnidia are 
gicbose; the pycnospores are hyaline, needle-shaped, 
many-septate, and lose their vitality when exposed 
to ordinary room temperature for about four days. 

Control. The disease often starts on the seedlings 
in the seed bed. It is important, therefore, to start 
with a clean seed bed soil. Seedlings should be 
sprayed with 4-4-50 Bordeaux before being trans- 
planted. In the house, the plants should not be 
worked when wet. Spraying with 4-4-50 Bordeaux 
IS recommended. 

Anthracnose 

Caused by Colletotrichum phomoides (Sacc.) 
Chester. 

Anthracnose is a disease to which ripe tomatoes 
are especially subject. The losses are often con- 
siderable both in the house and in transit. 

Symptoms. The spots are at first small, but they 
soon enlarge. They are discolored, sunken, wrinkled, 
with distinct central zones, closely resembling the 
anthracnose of apple. In moist weather, the spots 
become coated with a salmon-colored layer which 
consists of the spores of the fungus. 

The Organism. In structure, C. phomoides is lit- 
tle different from other Colletotrichums. The seta 
of the fungus are very numerous, thus giving the 



192 Diseases of Greenhouse Crops 



acervuli a black appearance. The conidiophores are 
short, and the conidia, oblong, hyaline and one- 
celled. 

Control, Anthracnose depends upon a moist at- 
mosphere for its activity. Spraying with Bordeaux 
is recommended. 

Leaf Mold 

Caused by Cladosporium fulvum Cke. 

Leaf mold is very troublesome in the greenhouse. 
In some of the Southern States, however, it is found 
on field tomatoes also. The disease is favored by 
a damp, moist atmosphere. 

Symptoms, The mold appears as rusty cinnamon, 
colored irregular, feltlike spots on the underside of 
the leaf (fig. 36, b), the upper part of which turns 
brown, then black. The affected foliage finally curls 
and dies. 

The Organism. The conidiophores of the fungus 
break through the cuticle of the epidermis in a dense 
crowded mass. The conidia are few and are borne 
on the tip ends of the condiophores, which are spar- 
ingly branched and knotty. The conidia are elliptic 
or oblong (fig. 36, c), 1 septate. 

Control. The effects of the disease are seldom 
disastrous if infection starts when the fruit has set 
and is well developed. An early infection when 
the plants are still young may result in the failure 
of the crop. Careful and thorough spraying with 
Bordeaux 4-4-50 before the disease appears is rec- 
ommended. Spraying should be done once every 



Tomato Diseases 193 



two weeks and should cease about five days before 
the fruit is picked. If the disease becomes well es- 
tablished in a house, spraying will prove of little 
benefit. In that case, the house should be emptied 
of all vegetation, the soil sterilized with steam or 
formaldehyde (see pp. 32-43), and wherever possi- 
ble the house, too, should be fumigated with formal- 
dehyde and potassium permanganate (see p. 164). 

Black Rot 

Caused by Macrosporium solani E. and M. 

Symptoms, Black rot is a fruit, stem, and foliage 
trouble. The spots are black, dry, slightly wrinkled, 
and extend deep into the interior tissue (fig. 37, a 
and b.). 

The Organism. The mycelium of the fungus at 
first varies in hue from hyaline to brown, then turns 
black. The conidiophores and conidia are dark, 
with three to six transverse and one to two longi- 
tudinal septse (fig. 37, c). Spraying with Bordeaux 
mixture is recommended. 

Sleeping Sickness 

Caused by Fusarium lycopersici Sacc. 

Sleeping sickness is a tomato trouble. It is usu- 
ally brought in with diseased seedlings. 

Symptoms, Infected plants become pale, the 
leaves wilt and droop and never recover (fig. 38, 
a.). The droopiness of a diseased plant gives it a 



194 Diseases of Greenhouse Crops 



sleepy appearance, hence the name of the disease. 
On splitting open a diseased root or stem, one finds 
that the interior vascular bundles are brown, due 
to the presence of the parasite (fig. 38, b.). 

The Organism. F. ly coper sici is a soil fungus 
which may be introduced with infected manure or 
seedlings. The fungus greatly resembles F. oxy- 
sporum. The conidia are hyaline to yellowish, fal- 
cate, acute (fig. 38, c and d.). 

Control, Spraying will not control this malady 
since the parasite lives internally and cannot be 
reached by external applications. The selection of 
resistant varieties may offer a means of conquering 
this trouble. Soil sterilization with steam or for- 
maldehyde is essential. 

Black Mold 

Caused by Fumago vagans Pers. 

Black mold usually follows the attacks of the 
white fly. The same fungus also attacks nastur- 
tiums grown indoors. The fungus appears as a con- 
spicuous olive-black growth on the upper part of 
the leaves. The fungus in this case is not parasitic, 
but usually grows on the honey dew secreted by the 
white fly. Although the fungus is not parasitic, its 
presence on the leaves is undesirable since it inter- 
feres with the absorption of light by the plant. In 
controlling white fly, the black mold fungus will also 
be checked. 



Tomato Diseases 195 



Rhizoctonia Fruit Rot 

Caused by Corticium vagum B. and C. var. solani 
Burt. 

This form of rot makes its appearance at the 
place where the fruit touches the ground. The dis- 
eased area becomes chocolate-colored, and the epi- 
dermis slightly wrinkled. The rot extends into the 
interior pulp, turning it brown and dry. For a 
further description of the causative fungus, see 
p. 20. 

Root Knot, see Nematode, p. 28. 

Broom Rape 

Caused by Orobanche ramosa L. 

The parasite fastens itself to the tomato roots 
whence it derives its food. The parasite produces 
a base of considerable size below ground from which 
a cluster of branching stems and bluish-yellow flow- 
ers appear above ground. The same parasite also 
attacks the hemp and tobacco out of doors. 

Fumigation Against White Fly 

The tomato is a favorite host for the white fly. 

The different conflicting results obtained by grow- 
ers in the fumigation treatment may be attributed to 
the use of widely different varieties of plants. The 
variations may also be partly due to tightness or 
looseness in construction of the greenhouse. Inves- 



196 Diseases of Greenhouse Crops 



tigations by Warren and Voorhees"^ have shown that 
tomato varieties such as Lester Prolific, Elongated 
Sparks, Earliana and Station Yellow recover from 
the first fumigation with almost no injury. Under 
the same treatment. Eclipse and Fragmore's Selected 
suffer lightly, while Stone, Lorillard, Beauty, Per- 
fection, and Best of All become seriously injured. 
Tomato plants injured by night fumigation usually 
show no ill effect until about four o'clock the follow-* 
ing day, when they wilt. If lightly injured the tops 
usually die. Fumigation for fifteen minutes with 
potassium cyanide, one ounce to each 1,000 cubic 
feet of glass, during the dark is 'satisfactory for 
indoor tomatoes. The house at that time should be 
cool and dry (fig. 39, a-c). 

•Warren, G. F., and Voorhees, J. A., New Jersey Agr. Expt 
Sta. Twenty-seventh Ann. Rept.: 242-246, 1906. 



PART IV 
DISEASES OF ORNAMENTALS 



CHAPTER 17 



ALTERNANTHERA {Altemanthera sp.) 

Cultural Considerations^ see Coleus, p. 245. 

Diseases of the Alternanthera 

The Alternanthera is comparatively free from dis- 
ease and it is generally considered a hardy plant. 

Leaf Blight 

Caused by Phyllosticta sp. 

Symptoms, Alternanthera blight was first re- 
ported by Halsted* as being very serious in green- 
houses of the eastern states. It is especially severe 
in the "cutting" benches. The trouble is character- 
ized by a premature defoliation. The affected 
leaves coil up and drop o£E. In an early stage, the 
leaves become spotted merely, and it is only when 
the spots become numerous that the foliage drops 
off. The trouble is usually overlooked, because of 
the variegated foliage of the host. The cause of 
the blight is a Phyllosticta fungus, probably the same 

♦Halsted, B. D., New Jersey Agr. Expt. Sta., Thirteenth Ann. 
Kept: 299, 1892. 

199 



200 Diseases of Greenhouse Crops 



as P. amaranthi^ which attacks the pigweed, Amaran- 
thus retroflexus. 

Control. It is probable that spraying with a 
standard fungicide will control the trouble. 

Root Rot 

Caused by Rhizoctonia solani Kuhn. 

This form of injury is commonly met with in 
propagating benches of Alternanthera. The young 
cuttings often rot off before setting roots. On well 
established plants, the Rhizoctonia fungus is found 
as strands on the sides of the branches which touch 
the ground. In this case there is apparently no in- 
jury. It seems that the reddish varieties of Alter- 
nanthera is covered with more Rhizoctonia strands 
than are the green or the variegated varieties. For 
a description of the causal organism and methods 
of control, see p. 20. 

Antirrhinum {Antirrhinum Majus), 

Cultural Co7 iderations. Antirrhinums have be- 
come important plants, forced primarily as cut 
flowers. The plants require a light sandy loam com- 
post. In filling the benches, we must avoid fresh 
and undecomposed manure. It is necessary also to 
avoid the excessive use of nitrogen. Where this is 
overlooked, the flowers will have a tendency to 
"sport" and possess too much yellow color, which is 
objectionable to the trade. Some growers prefer to 



Antirrhinum Diseases 20i 



add to the soil a liberal application of rock phosphate 
and finely ground limestone. Antirrhinums thrive 
very poorly in wet soils. The plants should not be 
syringed in winter and especial care should be taken 
in watering on cloudy days. The plants are not in- 
jured by a night temperature of 45 degrees F., al- 
though 48 to 55 degrees suits them best. The day 
temperature should never run above 70 degrees F. 

Diseases of the Antirrhinum 

The antirrhinum, although considered a hardy 
plant, is subject to several diseases, most of which 
are of economic importance. 

Rust 

Caused by Puccinia antirrhini Diet, and Halw. 

Symptoms, The Uredo stage is the one most 
commonly found. It is manifested as small round- 
ish, reddish brown pustules, usually grouped circu- 
larly on the under side of the leaf or on the stem 
(fig. 40, a and b). The affected tissue becomes yel- 
low. The fungus was first described by Dietel* who 
found the Teleuto and the Uredo stage on specimens 
collected in California. The fungus is very com- 
monly found to attack snapdragons out of doors. 
It is also a serious trouble to growers of greenhouse 
plants. However, the Teleuto stage is not fre- 

•Hedwigia, 36:298, 1897. 



202 Diseases of Greenhouse Crops 

quently met with. The exact life history of this 
fungus is as yet imperfectly known. 

Control, In the greenhouse, the disease is only 
prevalent on snapdragon propagated by cuttings 
taken from outdoor plants. In this case, the dis- 
ease is brought in directly with infected cuttings. 
The only remedy known is to use healthy cuttings. 
The safest is to use plants started from seeds sown 
indoors. 

Anthracnose 

Caused by Colletotrichum antirrhini Stew. 

Symptoms. Anthracnose is a common disease on 
greenhouse and garden snapdragons. In the green- 
house, it is more troublesome in the fall and spring. 
The disease attacks the stems (fig. 40, d) in all 
stages of development. It appears as a large spot 
on the stems or lateral shoots, resulting in their 
death (fig. 41, a and b). The spots are at first dirty 
white with a narrow border. Soon, however, the 
center turns black and under conditions of moisture, 
becomes covered with the acervuli of the causal or- 
ganism. On the leaves (fig. 40, d) the spots are 
circular, slightly sunken, at first yellowish green 
with indefinite outline, and later becoming dirty 
white or greenish, definitely outlined and limited 
by a narrow brown border. The spots, when nu- 
merous, spread and blend together. The affected 
foliage shrivels, clings to the stems and dies. 




Fig. 40. Antirrhinum Diseases. 

a. Rust on leaves, h. root knot, c. Uredo spores of Puccinia antir- 
rhini (after Schwarze), d. anthracnose lesions on stems and leaves, e. sec- 
tion through an acervulus of CoUetotrichiim antirrhini f. spores of C. 
antirrhini, (d-f after Stewart, F. C). 



Antirrhinum Diseases 203 



The Organism. The stroma is well developed; 
the conidia are straight to curved, with both ends 
rounded. The conidiophores are short, the setse 
abundant, dark brown, simple, and mostly straight 
(hg. 40, e and f). 

ControL The disease is often introduced in the 
greenhouse with infected cuttings. Cuttings should 
therefore be secured from healthy plants. This 
disease attacks only the snapdragon. It should 
therefore be an easy matter to prevent its introduc- 
tion indoors. If the disease makes its appearance, 
spraying with Bordeaux mixture should be resorted 
to. All diseased material should be destroyed by 
fire. 

Branch Blight 

Caused by Phoma poolensis Taub. 

Symptoms, The disease seems to be confined to 
the tender and growing shoots. It seldom affects 
the older and more woody stems. Affected parts 
wilt, and become discolored without showing any 
definite spotting. Later, however, numerous pycni- 
dia appear on the dead parts. 

The Organism. — Stewart* has proved by artificial 
inoculation that the causal organism is a parasite. 
The writer's investigation of this organism has con- 
firmed the work of Stewart. In 1916 and 1917, a 
careful study of this disease was made, as it occurred 
in several greenhouse establishments in San Antonio, 

♦Stewart, F. C, New York (Geneva) Agr. Expt. Sta. Bui. 
179: X09-110, 1900. 



204 Diseases of Greenhouse Crops 



Texas. It was proved definitely that the organism is 
parasitic and that it was also apparently an unde- 
scribed species to which the name Fhoma poolensis 
Taubenhaus was given. The pycnidia are minute, 
numerous, black, with distinct mouths (ostioles). 
The spores ooze out in a colorless gelatinous rope- 
like mass. They are small, elliptical, hyaline, and 
one celled. 

ControL The methods of control for this disease 
should be the same as those used for anthracnose. 

Blight 

Caused by Septoria antirrhini Desm. 

This disease is greatly dreaded by English gar- 
deners. It was first described by Chittenden* who 
claims that it is very prevalent in Great Britain. 
Fortunately, it is not yet known to occur in the 
United States. The disease is characterized by a 
general blighting and dying of the leaves and 
branches. 

Wilt 

Caused by Verticillium sp. 

This disease, although new, is prevalent all over 
the United States. Little is known of the disease 
and of the causal organism. The Verticillium, how- 
ever, may be introduced with infected soil or ma- 
nure, or with diseased cuttings. To prevent the 

♦Chittenden, J. F., Jour. Roy. Hort. Soc. 35: 216-217, 1909. 




Fig. 41. AxTiKRHixuM Diseases. 

a. Healthy plant, b. plant killed by anthracnose (a and b after Stewart, F. C). 



Aspidistra Diseases 205 



disease from getting a foothold in the greenhouse, 
it is necessary to secure cuttings from healthy plants. 
Infected soils should be steam sterilized or treated 
with formaldehyde (see pp. 32-43). Spraying in 
this case will be useless since the causal organism 
works in the interior of the roots and stems. 
Root Knot (fig. 40, b), see Nematode, p. 28. 

Aspidistra (^Aspidistra Lurida) 

Cultural Considerations. This plant is very easy 
to grow. It is valued mostly as a foliage plant. It 
grows well in dark halls and in dwelling houses. 
The plant requires an abundance of water. It is 
propagated by division of rhizomes in late winter. 

Diseases of Aspidistra 

The Aspidistra is a very hardy plant. It is sub- 
ject to the attacks of but few diseases. 

Anthracnose 

Caused by Colletotrichum omnivorum Hals. 

This disease causes irregular ragged dry spots on 
the leaves. The spores are sickle shaped, hyaline, 
one celled. The setse are black, elongate, and 
pointed. The disease may be kept in check by 
spraying with a standard fungicide. All infected 
material should be destroyed by fire. 



2o6 Diseases of Greenhouse Crops 



Leaf Spot 

Caused by Ascochyta aspidistra Mas. 

This disease is characterized by roundish, whit- 
ish spots on the leaves. The trouble is as yet of no 
economic importance. Little is known of the causal 
organisms. Of the other fungi recorded on aspidis- 
tra may be mentioned Fyrenochczta bergevini Roll. 



CHAPTER 18 



ASTER (Aster sp.) 

Cultural Considerations^ see Chrysanthemum, p. 
235. 

Diseases of the Aster 

Although considered a hardy plant, asters are sub- 
ject to some important diseases when grown under 
greenhouse conditions. 

Yellows 
Cause, physiological. 

Symptoms. This is a very obscure disease, the 
cause of which is little understood. It has been in- 
vestigated by Smith, who, however, reached no 
definite conclusions. The roots of affected plants 
are apparently normal in every respect. The stems 
and branches, however, become pale yellow, slender 
and spindly, and in extreme cases stunted. The 
leaves too are often stunted and poorly developed. 
The flower bracts show no change, the calyx (se- 
pals) has a tendency to revert to leaf-like lobes. 
The color of the corolla changes to a uniform light 
greenish yellow irrespective of the original color of 

* Smith, R. E., Mass. (Hatch) Agr. Expt. Sta., Bui. 79: 3-26, 1902. 

207 



2o8 Diseases of Greenhouse Crops 



the variety. In fonii, the florets of the corolla be- 
come elongated, tubular, with short lobes at the 
ends. The stamens have a tendency to abort, the 
anthers are undersized, producing little or no pol- 
len. The pistil tends to elongate, the stigma too 
becomes much elongated and enlarged, protruding 
abnormally from the corolla tube. The ovary and 
ovules too are elongated and enlarged (fig. 42, a and 
b). Affected plants produce no seeds. The same 
disease also attacks the Marguerite, the Calendula, 
and the African Marigold. The cause of the trouble 
is unknown. Practically all varieties of asters are 
equally susceptible. The source of the seed, its stor- 
age conditions, transplanting, the physical proper- 
ties of the soil, are not apparently concerned in the 
development of this malady. 

Control, It is very likely that yellows may have 
an origin similar to that of mosaic. In the latter 
case, insects are likely to carry and to spread the 
virus. The control of all insect pests is therefore 
recommended. Diseased plants should be pulled 
out and destroyed by fire. Spraying will be of no 
benefit. 

Leaf Blight 

Caused by Bacillus asteracearum Pava. 
The disease is known to occur in Italy where it 
was described by Pavarino."^ The trouble is ap- 

*Pavarino, G. L., Atti. K Accad. Lencei Rend. CI. Sci. Fis., 
Mat. et Nat. 21: 544-546, 1912. 



Fig. 42. Aster Diseases. 

a. Blossoms affected with yellows, notice the one-sidedness of the 
petals, b. section of a partially diseased blossom, showing upward turn 
of affected florets, c. young plant affected with Fusarium wilt (a-c after 
Smith, R. E.). 



Aster Diseases 209 



parently confined to the foliage, the lower leaves 
usually becoming infected first, then dry and shrivel. 
Leaf blight is as yet of no importance in this coun- 
try. 

Wilt or Stem Rot 
Caused by Fusarium sp. 

Symptoms. This disease appears as soon as the 
plants are set out and persists throughout the grow- 
ing season. It is, however, most noticeable during 
planting time and at blossoming. The trouble usu- 
ally becomes apparent first on the lower leaves. 
Here the normal color disappears, turning to a dull 
yellowish green, followed by wilting. This seems 
to spread throughout the length of the stem although 
the disease is usually confined to one side of the 
plant (fig. 42, c). This gives it a very characteris- 
tic appearance, since one side of the plant has a 
dull-green, wilted, blighted appearance and only 
one half of some of the leaves and flowers are af- 
fected at first. When pulled up, the roots and stems 
of a diseased plant appear perfectly healthy. 
However, if one splits open lengthwise the stem of 
an infected plant, he will find that the seat of the 
trouble is localized in the interior of the woody or 
vascular tissue, the latter of which will be darkened. 
Infection in this case no doubt takes place in the 
seed, at the seedling stage. Although some plants are 
able to make a little headway in spite of the dis- 
ease they too finally succumb. The cause of the 



210 Diseases of Greenhouse Crops 

trouble is a Fusarium fungus, of which little is now 
known. 

Control. Since the Fusarium fungus is a soil in- 
habiting organism, steam sterilization of the soil at 
once suggests itself. The seed should always be 
started on a sterilized soil, and this trouble will be 
entirely eliminated. Diseased plants should be 
pulled out and burned, and by no means allowed to 
find their way into the manure pile. Spraying in 
this case will be of no value, since the seat of the 
trouble is confined to the interior of the roots and 
stems. 

Otlier Troubles Mistaken for Wilt. An injury in- 
flicted by the common white grub (Lachnosterna) 
is often mistaken for wilt. The latter feeds on the 
roots, and the result is a general wilting. When the 
affected plant is pulled up, the grubs will be found 
in the act of feeding. By careful watching, they 
may be destroyed before serious damage results to 
the plants. 

Another cause of apparent wilt and stunted 
growth may be due to the sucking of the root lice. 
The latter are of a bluish color, and are usually 
found in large number on a single plant. This pest 
usually is harbored in the soil, especially where as- 
ters are continually grown in the same beds. Chang- 
ing the soil or sterilizing it with steam will effect a 
cure. 

In Europe, Fusarium incarnatum (Desm.) Sacc. 
is believed to be the cause of an aster wilt there. 



Aster Diseases 211 



Damping Off 

Caused by Rhizoctonia solani Kuhn. 

Symptoms. The trouble is at first manifested as 
brownish spots on one side of the seedlings at the 
surface of the soil. The lesions increase in size until 
the seedlings are girdled and topple over. In time, 
the Rhizoctonia fungus spreads over the fallen 
plants and forms a mat of mycelia over them. 

On older aster plants, a damping off is not pro- 
duced, but instead the typical Rhizoctonia lesions 
appear on the stem end and on the roots. For a 
description of the causal organism and methods of 
control, see p. 20. 

Root Knot 

Caused by Heterodera radicicola Muhler. 

Symptoms, The disease manifests itself when 
the plants are about three inches high. The younger 
portions of the plant produce spindly shoots with 
dwarfed, disfigured leaves. The color of this growth 
is yellowish pale to white, the flowers are small and 
stunted. Such plants are known to florists as "white 
legs." For a description of the organism and meth- 
ods of control see Nematode, p. 28. 

Azalea (^Azalea Indica) 

Cultural Considerations, Azaleas are very sensitive 
as regards water. They require plenty of moisture, 



212 Diseases of Greenhouse Crops 

but not so much as to make the soil soggy. They 
demand a cool, shady house and a rather close at- 
mosphere. The varieties forced for the Easter mar- 
ket should be kept in a temperature of 45 to 50 de- 
grees F., and those forced for Christmas should be 
grown under a temperature of 50 to 55 degrees. Six 
to eight weeks before Christmas the plants are given 
a temperature of 60 to 65 degrees F. In providing 
ventilation, cold drafts should be avoided. The best 
time to re-pot azaleas is after blooming. Neglect 
in this direction may seriously interfere with next 
year's bloom. Azaleas are very sensitive and may be 
injured even by the presence of organic matter of a 
heat producing nature. This means that the ma- 
nure in the compost must be thoroughly rotted. 

Diseases of Azalea 

The literature on azalea diseases is very scant. 
This means either that the troubles of this plant are 
still to be investigated or that it is a remarkably 
healthy one. 

Leaf Spot 

Caused by Septoria Azale^z Vogl. 

Symptoms. This disease is characterized by red- 
dish yellow spots on the leaves. It is not of great 
importance economically. 

The Organism. The pycnidia are immersed, glo- 
bose, depressed, black. The conidia are oblong, fili- 
form, straight or curved, 1 to 3 or more septate, and 




Fig. 43. Begonia Root Knot. 



Begonia Diseases 213 



constricted slightly at the septum. The Conidio- 
phores are short and cylindric. 

The Begonia {Begonia sp.) 

Cultural Considerations, Begonias have become 
a very popular plant commercially. The tuberous 
type is extensively grown under glass. Throughout 
the season, the plants require frequent applications 
of liquid cow manure. They require an abundance 
of light and air, but are very sensitive to draughts 
and to exposure to direct sunlight. The best tem- 
perature required is about 65 degrees F. In the 
summer, the house should be frequently syringed in 
order to keep it cool. 

Diseases of the Begonias 

Begonias, although considered hardy plants, are 
subject to a few important diseases. 

Powdery Mildew 
Caused by Oidium sp. 

Stewart* records a powdery mildew attacking the 
stems but not the leaves of begonia. The trouble 
appears as a white powdery fungus growth charac- 
teristic of all similar mildews. Only the Oidium 
or conidial stage of the fungus is present. It is not 

♦Stewart, F. C, New York (Geneva) Agr. Expt Sta. Bui. 328: 
331, 1910- 



214 Diseases of Greenhouse Crops 



likely that this disease will become troublesome in 
greenhouses where begonia is grown on a large scale. 

Root Rot 

Caused by Rhizoctonia solani Kuhn. 

The symptoms of root rot on begonia are the 
same as those described for alternanthera. The fun- 
gus also causes a damping off disease on young be- 
gonia cuttings. 

Root Knot (fig. 43), see Nematode, p. 28. 

Caladium {Caladium sp,) 

Cultural Considerations. Caladiums should never 
be allowed to become pot bound. They require a 
medium temperature, plenty of water, ventilation, 
and drainage. As the growing season is over and 
the plants lose their leaves, the pots should be laid 
on their sides and the water withheld sufficiently 
to prevent growth. 

Diseases of the Caladium 

Caladiums, it seems, are very hardy. The fungi 
recorded on matured parts of this plant may be men- 
tioned : 

Cercospora caladii Cke., Macrophoma surinamen' 
sis (B. and C.) Berl. and Vogl., Monilia prunosa 
Cke. and Mass.; Sphd^rella caladii (Schw.) Sacc, 
Uromyces caladii (Schew.) Farl. 



Fig. 44. CoLCEOLARiA Leaf Blight (After Halsted). 



Calceolaria Diseases 215 



Calceolaria (^Calceolaria aracknoided) 

Cultural Considerations, Calceolarise are green- 
house annuals grown for decorative purposes. It 
requires a soil made of equal parts of leaf mold, 
sand, and sand loam. The plants require frequent 
repotting to prevent them from becoming potbound, 
although the flowers are usually better when pot- 
bound. The plants require a northern exposure dur- 
ing the summer, plenty of ventilation, and a cool 
house. A temperature of 70 degrees F. may seri- 
ously injure them. Partial shading should be pro- 
vided, and no water should be permitted to accu- 
mulate on the foliage. 

Diseases of the Calceolaria 

The Calceolaria is apparently a very resistant 
plant. Halsted,"^ however, records a leaf blight that 
affects it. The trouble appears as brownish patches 
on the leaves just about blossoming time. The 
patches are many sided and seem to be bound by 
the smaller veins of the leaf (fig. 44). The spots 
are water-soaked, and transparent when held against 
any light. The cause of this trouble seems to be a 
bacterial organism which, however, needs further in- 
vestigation. The same is true for methods of con- 
trol. 

♦Halsted, B. D., New Jersey Agr. Expt. Sta., 14th Ann. Rept.: 
430-431, 1893. 



2i6 Diseases of Greenhouse Crops 



Canna (^Carina indica) 

Cultural Considerations, The canna, although an 
outdoor plant, is also extensively grown in the green- 
house for propagation and for decoration. The va- 
rieties best adapted for forcing may be mentioned: 
Queen Charlotte, Madame Crazy, Explorateur. For 
flowering in the greenhouse it is best to start with 
dormant plants. 

Fungi Recorded on the Canna 

Cannas seem to be unusually free from diseases. 
With the exception perhaps of the rust, Uredo can- 
ncz^ the others here mentioned are saprophytes or 
semi-saprophytes attacking old and weakened plants. 

Anthostomella achira Speg., Macros porium huU 
botrichum Cke., Ophiobolus linosporoides Speg., 
Uredo canncz Wint. 



CHAPTER 19 



THE CARNATION {Diauthus curyophyllus) 

Cultural Considerations. The general trend of 
cultural operations in the greenhouse (fig. 45) 
should be toward the production of a healthy, 
vigorous growth. The cutting itself will, to a cer- 
tain extent, predetermine the health of the plant. 
Cuttings should not be weak to begin with. Those 
which are firm, but also somewhat soft, are desirable. 
The best cuttings are usually made from the strong 
pips along the sides of the stems. As soon as the 
cuttings have developed roots in the propagating 
bed, they are usually transplanted into pots or into 
flats. In either case, they should not be planted too 
deeply in the soil. Deeply set cuttings are more 
subject to stem rot, especially when overwatered. 
As the cuttings develop they should not be permit- 
ted to become pot bound. By keeping them in a 
comparatively low temperature, the formation of 
soft succulent growth will be prevented. With 
many growers, carnations are grown in the field for 
a time. This practically insures vigorous growth as 
it develops a certain hardiness and resistance to dis- 
ease. Where land is scarce, carnations are grown 
indoors in the summer. Such plants, however, are 

217 



2i8 Diseases of Greenhouse Crops 



found to be weak and susceptible to disease. In first 
pinching back the plants to encourage spreading, it 
should be done in such a way that the plants will 
branch some distance above the surface of the soil. 
In other words, the farther the stems are from the 
ground the more protected the plant is from disease. 
When the plants are permanently set for the winter, 
heavy watering should be avoided. Too much water 
compacts the soil, excludes air, and retards normal 
root development. As the plants become well es- 
tablished, and especially during the hot days of Sep- 
tember and October, as well as in the spring, they 
should not be permitted to suffer from a lack of 
water. This is especially true in raised benches with 
the heating pipes directly underneath. In this case, 
the surface soil may appear wet, yet the soil be- 
neath may be as dry as possible. On the other hand 
serious injury may occur from overwatering, espe- 
cially in solid benches on cloudy days. The night 
temperature of the carnation house should be about 
fifty degrees F. At sixty degrees the plants will be 
stimulated to slightly earlier blooming, but the 
blooms will be small, and the plant subject to a 
more rapid exhaustion. At a night temperature of 
40 degrees F. blooming will undoubtedly be re- 
tarded although the plants will be stockier and last 
longer. The day temperature of the house should 
be decided upon according to outside weather condi- 
tions. On a clear day and when sufficient ventila- 
tion is given, the temperature may run from 65 to 75 
degrees F. 



Carnation Diseases 219 



Diseases of the Carnation 

White Tip 
Cause, gas injury. 

Symptoms, The trouble appears as a white or 
creamy coloring of the unrolled tender tips of the 
foliage (fig. 46, a). Occasionally, the white spots 
appear across the leaves a short distance below the 
tips. The cause of the injury is believed by Clin- 
ton"^ to be due to gas rather than to spray injury. 
The trouble may be brought about by the fumes of 
sulphur or tobacco used as an insecticide or fungi- 
cide. The injury affects the tip because of the ten- 
derness of the tissue there. The Enchantress is par- 
ticularly susceptible to it. The secret of its suc- 
cessful control lies in the care exercised during fumi- 
gation. 

Sleep 

Cause, gas injury. 

Growers in the vicinity of large manufacturing 
plants are often troubled with what is called sleep 
of carnation. This trouble is especially common in 
cities where gas is used for illumination. The 
symptom of sleep is a closing inward of the petals 
(opened corolla). Once a blossom goes to sleep it 
never opens again. The investigations by Crocker 
and Knight t have shown that at least one cause of 
sleep in carnation is due to traces of illuminating 

♦Clinton, G. P., Conn. Agr. Expt. Sta., Thirty-ninth Ann. Rept.: 
428-429, 1915. 

t Crocker, W., and Knight, L., Bot. Gaz. 56:259-276, 1908. 



220 Diseases of Greenhouse Crops 



gas (ethylene) in the surrounding atmosphere. This 
trouble has been overcome in floral establishments 
where lighting gas was replaced by electricity. 

Malnutrition 
Cause, overfeeding. 

Symptoms. The trouble is usually manifested on 
the blossoms. It is brought about by the applica- 
tion of an excess of certain chemical fertilizers. 
Acid phosphate applied in large quantities seems to 
produce no injury. An excess of dried blood will 
produce blossoms which become soft and subject to 
sunburn if sprinkled during sunshiny weather. Later, 
such injured blossoms have their center petals 
bunched, and only a few others opening. Later, 
the buds fail to open, the foliage assumes a deep 
green color with abundant glossiness and a normal 
growth. If overfeeding is continued growth ceases. 
Plants thus affected may, however, recover with ju- 
dicious feeding. 

Overfeeding with potassium sulphate is decidedly 
unfavorable. The edges of the inner petals crinkle, 
brown spots appear, and often there is a withering 
of the edges of the petals, while the center ones fail 
to open, as though glued together. The unopened 
buds swell, and the pistil is commonly seen project- 
ing one inch beyond the bud. Moreover, there is a 
retarded growth, the leaf tips begin to die, and the 
whole plant resembles a rosette. 



Carnation Diseases 221 



Splitting of Blossoms 
Cause, underfeeding. 

Carnation growers often lose heavily from the 
splitting of blossoms just before they fully open. 
The investigations of Darner"^ and others seem to 
show that the splitting is brought about by under- 
feeding. The moderate application of commercial 
fertilizers will not cause an increase in splitting and 
may cause a decrease. 

The splitting of the blossoms may also be noticed 
on the row of carnations near the glass of the side 
benches. The cause, it is assumed in this case, is 
due to the more rapid drying of the soil of the 
benches nearest the glass. Growers often prevent 
this trouble by so placing the benches as to allow 
a walk between them and the side walls. 

Yellows 

Cause unknown. 

Symptoms. True yellows as described by Lam- 
key t appears as a yellowing (mottled chlorosis) on 
the leaves. The mottling is brought about by the 
presence of indefinite irregular blotches or flecks 
which meet and form yellow streaks. The mottling 
is more comm_on on the younger leaves, and the 
streaks on the older ones. The yellow areas may 
become red or pink. The spots are never water- 

♦Darner, H. B., et al., Illinois Agr. Sta. Bui. 176: 378-379, 1914. 
tLarakey, M. R., The American Flor. 58:508-510, 1917. 



222 Diseases of Greenhouse Crops 



soaked and possess no watery margin. They are 
always sunken, and possess no definite center. The 
cause of the trouble does not seem to be associated 
with any parasitic organism, but is probably due to 
improper cultural conditions, the exact nature of 
which is unknown. 

Control. The control for yellows, as recom- 
mended by Peltier"^ is as follows : Every check which 
tends to lower the vitality of the plant should be 
avoided. Weaker plants are more subject to yellows 
than stronger ones. Cuttings should never be taken 
from plants showing yellows. They should be made, 
too, from plants in bloom rather than from stock 
plants. They should be rooted early and should not 
be permitted to remain too long in the sand after 
rooting. The later the cuttings are made, the longer 
they take to root, and the more susceptible they 
are to yellows. Young plants should not be allowed 
to become pot bound. 

Cohesion of Petals 
Cause unknown. 

Carnation growers are often troubled by what is 
generally termed cohesion of petals. The latter are 
well out of the calyx, but are stuck together. Often 
they are grown together to such an extent that it is 
impossible to separate them without tearing the 
tissue. The trouble was first described by Arthur,t 
but the exact cause of it is as yet unknown. 

♦Peltier, G. L,, The American Flor. 46: 725-726, 1906 
t Arthur, J. C, Proc. Amer. Carnation Soc, 1896. 




Fig. 46. Carnation Diseases. 

a. White tip (after Clinton), b-f. carnation rust parasite (after 
Blodgett, F. H.), g. stigmanose (after Woods), h. Septoria leaf 
spot (after Potter, M. C), i. pycnidia of Septoria dianthi, j. pow- 
dery mildew fungus (after Mercer, W. B.). 



Carnation Diseases 223 



Stigmonose 
Caused by insect sting. 

Symptoms. The best symptoms of this disease 
are manifested on the younger, but full-sized leaves 
nearest the upper end of the stem. A casual glance 
at such leaves reveals little to the untrained eye. 
However, by holding them near the sunlight, small 
dots may be seen scattered. These dots have a faint 
yellowish color. Later the surface tissue dries and 
the dots assume a whitish, reddish, or purplish 
color, while the spots enlarge and become sunken 
(fig. 46, g.). Such spots are seldom dark colored 
in the center nor are they made up of concentric 
rings. With the increase of the spots, the leaves 
wither, but cling to the stems. The general effect 
of stigmonose is a premature yellowing and stunt- 
ing of the plant. The vigor of the plant at the time 
of the appearance of the disease largely determines 
the severity of the injury. Strong plants will be- 
come spotted, but will in no other way greatly suffer 
from it. Weak plants of the same variety will be- 
come stunted, and in many cases seldom outgrow 
the disease. 

The cause of the disease was first attributed by 
Arthur and Bolley"^ to a bacterial organism BaC' 
terium dianthi Arthur and Bolley. However, the 
investigations of Woods t show that stigmonose is 

•Arthur, J. C, and Bolley, H. L., Indiana Agr. Expt. Sta. Bui. 
59: 17-38, 1896. 

t Woods, A. F., U. S. Dept. of Agr. Div. of Veg. Pathl. and 
Phys, Bui. 19: 7-30, 1900. 



224 Diseases of Greenhouse Crops 



caused by the stings of aphides, thrips, and red 
spiders. The irritant injected by these pests causes 
the cells to react and finally to collapse, resulting 
in the specking previously mentioned. 

Control. The carnation is a plant which is nat- 
urally adapted to a dry atmosphere. Under such 
conditions in the greenhouse aphides, thrips and 
red spiders are at their maximum activity. To keep 
these pests in check fumigation with tobacco ex- 
tracts or hydrocyanic acid gas is resorted to. The 
use of the latter, however, cannot be recommended 
for all carnation varieties. 

Rust 

Caused by Uromyces caryophyllinus (Schrank) 
Wint. 

Symptoms. The rust is readily recognized by ele- 
vated blisters or sori filled with brown spores. The 
sori are first covered by the epidermis of the host, 
but when they ripen the latter bursts open, liberat- 
ing the mature spores. This disease is more prev- 
alent in overheated and overwatered houses. In- 
fection once established will usually destroy a large 
per cent of the plants and seriously cripple many 
others. The disease may be found on all parts of 
the plant except the roots. Carnation rust seems to 
be more prevalent in the states lying east of the 
Alleghenies. Few greenhouses seem to be entirely 
free from the rust. 

The Organism. The fungus has two spore stages, 



Carnation Diseases 225 



the uredospores and teliospores, both of which forms 
greatly resemble each other. The iEcia are found 
on Euphorbia gerardiana in Europe and is recog- 
nized as Mcidium euphorbi erardiancz Fisch. The 
rust fungus attacks not only ine carnation, but sev- 
eral other species of the pink family. 

Control. Some florists advocate the use of an 
aqueous solution of common table salt. This is to 
be applied as a fine spray. Investigations by F. C. 
Stewart* have shown that salt solutions can neither 
prevent rust infection nor stimulate growth. Neither 
is it helpful to apply salt to the soil. Carnations 
are propagated chiefly by cuttings. The latter often 
carry the disease. It is, therefore, imperative that 
cuttings be taken from healthy plants. Maintain- 
ing the proper temperature and ventilation, as well 
as exercising care and judgment in watering, will 
help to keep this rust in check. Subirrigation is 
preferred to overhead irrigation to keep the plants 
dry. Progressive growers use an inverted V-shaped 
wire netting (one-inch mesh) placed between the 
rows. The wire is cut into strips of fifteen inches 
width. These are bent and inverted, about six inches 
high and eight inches wide, and placed between the 
rows of plants. This support to the foliage pre- 
vents it from touching the wet ground and admits 
at the same time perfect ventilation. It also makes 
it possible to water the soil without wetting the 
plants. The trouble may, of course, be avoided to 

♦Stewart, F. C, New York (Geneva) Agr. Expt. Sta., i6th 
Ann. Rept: 423-425, 1895. 



226 Diseases of Greenhouse Crops 



a great degree by growing resistant varieties. The 
Scott and the Jubilee are two varieties very sus- 
ceptible to rust. On tb ^ other hand, the Enchantress 
and the Lawson are h "^Vy resistant. 

A Parasite of Ca'j^,'^.^^i^on Rust. Most parasites 
have others to live on them. The carnation rust 
seems to be no exception. The fungus Darluca 
filum (Bin.) Cast, was found by Blodgett* to para- 
sitize the carnation rust fungus. The presence of 
the Darluca is manifested by a dwarfed and weak 
development of the rust pustules. The pycnidia of 
Darluca (fig. 46, b and c) are found scattered on 
the rust pustules and are flask shaped, the spores are 
two-celled (fig. 46, e and f), colorless, and when 
ripe escape in masses of long tendrils, held together 
by a gelatinous substance in the outer cell wall of the 
spore (fig. 46, d.). The latter readily germinate in 
water. Darluca filum also attacks the asparagus 
rust fungus. It is possible to grow Darluca in pure 
culture and to inoculate its spores on the carnation 
rust fungus. In nature, however, it has not proved 
abundant enough to keep the rust in check. 

Septoria Leaf Spot 

Caused by Septoria dianthi Desm. 

Symptoms, Leaf spot is characterized by light 
brown patches on the leaves and stems. On the 
latter, the spots are usually found midway between 

♦Blodgett, F. H., New York (Geneva) Agr. Expt. Sta., Bui. 
175: 1-13, 1900. 



Fig 47. Carnation Diseases. 

a. Healthy blossoms, b. blossoms affected with Sporotrichum rot (after 
Stewart, F. S. and Hodgkins), c. Heterosporium spot (after Smith, R. E.), 
e-d. Alternaria spot (after Stevens and Hall). 



Carnation Diseases 227 



the joints. On the leaves, infection seems to be 
more localized on the lower than on the upper half, 
and it is particularly frequent on the broad sheath- 
ing base of the leaf (fig. 46, h.). Affected foliage is 
often bent downwards. A leaf with numerous spots 
may be bent at various places, downward as well as 
sideways. The spots are usually indefinite in size 
and outline. Within the dead area may be found 
numerous minute fruiting bodies (pycnidia). 

Powdery Mildew 
Caused by Oidium sp. 

Mention of this disease is made by Mercer,^ who 
found it on greenhouse carnations in England. It 
has not yet proved of economic importance in the 
United States. This trouble appears as white, pow- 
dery patches on the leaves, calyx, and corolla. The 
English varieties most susceptible are "Lady Arling- 
ton," ''Bridesmaid," and especially "British Tri- 
umph." So far only the conidial or Oidium (fig. 
46, g) stage of the fungus is in evidence. The ascus 
or winter spore stage may probably appear on other 
hosts. The trouble may be kept in check by dust- 
ing with flowers of sulphur or by spraying with 
potassium sulphide as recommended for the rose 
mildew (see p. 323). 

♦Mercer, W. B., Jour. Roy. Hort. Soc. 41: 227-229, 1915. 



228 Diseases of Greenhouse Crops 



Bud Rot 

Caused by Sporothrichum po^ Pk. 

Symptoms, This disease seems to be confined to 
the floral buds only. Ordinarily the affected buds 
fail to expand or only open part way (fig. 47, a 
and b.). A close examination will show that the 
interior of the affected bud is browned and moldy. 
The rotted tissue may be found in the center of the 
bloom or on the petals. The stamens, styles, and 
pistils are also frequently affected. Where young 
buds are diseased the calyx, too, will be involved, 
otherwise it is usually sound, although the other 
parts of the flower may be decayed. 

The Organism. The hyphse are creeping, vary- 
ing in thickness, hyaline, and septate. The conidia 
are of two kinds : Microconidia — one-celled, globose 
or broadly ovate; Macroconidia — abundant, one, 
rarely two, septate and several times larger than the 
microconidia (fig. 48, g to i.). Stewart* claims 
that Sporotrichum pocz Peck found on diseased tops 
of June grass and ^S'. anthophilum^ which causes the 
bud rot of carnations are the same. The fungus is 
spread about in the greenhouse by a mite {Pedicu- 
lopsis graminum Reut.). 

Control. According to Heald t aoid others the 
most susceptible varieties to bud rot may be men- 
tioned — the Lawson, Enchantress, Queen Louise, 

* Stewart, F. C, and Hodgkiss, H. E., New York (Geneva) Agr. 
Expt. Sta. Tech. Bui. 7: 84-119, 1908. 

t Heald, F. D., Nebraska Agr. Expt. Sta., Bui. 103:3-31, 1908. 




Fig. 48. Carnation Diseases. 

a. Mycelium of Alternaria dianthi showing branching and septation, b. 
mycelium below stroma and hypheae emerging through the stroma, c. caten- 
ulate spores as borne upon hypheae, d. spores, e. an old cluster of conidio- 
phores, f. a young cluster of conidiophores (after Stevens and Hall),_ g. 
hypheae of Sporotrichum poae with immature spores on short tapering 
branches, h. typical spores of S. poae, i. germinating spore, /. Fusarium 
like spores of S poae, k. carnation blossom rotted, showing eggs of mites, 
/. female mite, m. male mite (after Stewart, F. C, and Hodgldss, H. E,). 



Carnation Diseases 229 



and Bradt. These, therefore, should be handled 
with more care. All diseased buds should be picked 
off and destroyed by fire. The temperature and 
moisture in the air should be kept as low as possi- 
ble. The fact that the mite which is associated 
with bud rot (fig. 48, k to m) is also found on 
June grass would suggest the necessity of avoiding 
sod where this grass is comxmon, in the making of 
the compost. This, however, may not be important 
when the soil is steam sterilized. 

Leaf Mold 

Caused by Heterosporium echinulatum Berk. 

Symptoms. The disease becomes apparent as 
roundish spots, varying from a sixteenth to a sixth 
of an inch in diameter, and is found mostly on the 
tip of the leaves. In severe cases the entire leaf 
and even the major tops of the plant become spotted 
(fig. 47, c). According to Halsted* the color of 
the spots is pale ashy and covered with a fine, dense 
growth of the causal fungus, giving it the moldy ap- 
pearance. Frequently the color changes to a gray 
shade, sometimes approaching dark brown. 

Alternaria Leaf Spot 

Caused by Alternaria dianthi Stevens and Hall. 
Symptoms, This trouble manifests itself as ashen 

*Halsted, B. D., New Jersey Agr. Expt Sta., Fourteenth Ann. 
Kept.: 386, 1893. 



230 Diseases of Greenhouse Crops 



white spots, the centers of which are occupied by a 
scanty or profuse black fungus growth, which is 
made up of the spores of the fungus (fig. 47, d 
and e.). The spots are dry, rather shrunken, circu- 
lar or somewhat elongated. If the node of the stem 
is attacked, the disease spreads sufficiently to involve 
the adjoining foliage as well. The stem itself be- 
comes somewhat girdled and in time is also killed. 
Usually, however, the spots are confined to the 
foliage. 

The Organism, The mycelium is dark brown, 
(fig. 48, a.). The conidiophores arise from a stroma, 
usually from one to twenty-five in number, and each 
one to four septate (fig. 48, b, e and f.). The coni- 
dia are borne in chains (fig. 48, d.), and in structure 
are very typical of other Altemarias (fig. 48, d.). 
The fungus grows well on various culture media. On 
media poor in sugars, the mycelium and spores are 
lighter in color and smaller in size and diameter. 

Control, All infected material should be collected 
and destroyed by fire. Spraying with a standard 
fungicide is also recommended. From the observa- 
tions of Stevens and Hall,* the variety Mrs. Thomas 
W. Lawson appears to be the most susceptible to this 
disease. As far as possible, this variety should be 
avoided. 

Anthracnose 
Caused by Volutella sp. 

Symptoms, The disease usually attacks the base 

* Stevens, F. L., and Hall, J. G., Bot. Gaz. 47:409-413, 1909. 



Carnation Diseases 231 



of the lower leaves as well as the stems which are 
closest to the ground. The trouble is seldom found 
on the upper leaves, although they may present a 
sickly pale appearance. Anthracnose is a serious 
disease of young cuttings. Not infrequently the 
grower loses 50 per cent of his cuttings from this 
disease. These damp off very quickly under a great 
variety of conditions. 

Damping Off 

Caused by Volutella leucotricha Atkinson. 

This disease seems to be confined mainly to carna- 
tion cuttings. The symptoms are not different from 
those of the damping off caused by other fungi. In 
this case, the causal organism, Volutella leucotricha^ 
first described by Atkinson, is distinct from V , 
dianthi Hals. The mycelium of the former has a 
tendency to swell at the hyphal cells, producing a 
strong constriction at the septa. The conidia of 
Volutella leucotricha are considerably smaller than 
those of V. dianthi and the setse are different in form 
and in color. In V . leucothrica they taper but little 
towards the free end, are blunt at the tip and many 
times septate, with the stroma light colored, while 
it is black in V , dianthi. The methods of control 
are the same as those for other damping off diseases 
(see p. 17). 

* Atkinson, G. P., New York (Cornell) Agr. Expt. Sta. Bui. 94: 
260-264, 1895. 



232 Diseases of Greenhouse Crops 



FusARiuM Leaf Spot 
Caused by Fusarium sp. 

Symptoms, This form of leaf spot usually fol- 
lows the injury caused by the rust fungus {Uromyces 
caryophyllinus). The variety Emily Pierson is es- 
pecially subject to the attacks of this peculiar leaf 
spot. The spots are large, often occupying the en- 
tire width of the leaf. The diseased tissue becomes 
covered with a pinkish mold in the center of which 
are found minute spore clusters of the Fusarium fun- 
gus. Little is known of the causal organism. In 
controlling rust, the leaf spot will also be kept in 
check. 

'Branch Rot," Dry Stem Rot, or Die Back 
Caused by Fusarium sp. 

Symptoms, This troublesome carnation disease 
was first described by Sturgis.* Attacked stems and 
branches wilt rapidly and the color of the leaves 
turns to a yellowish green. Dead stems remain firm, 
although wilted and shriveled. The bark likewise 
remains firm. The causal fungus seems to gain 
entrance through cuts or wounds. With cuttings 
the trouble may start at the base, causing them to 
dry up and to lose their normal color. The condi- 
tions which favor the disease are excessive rains 
in the summer when the plants grow out of doors. 
This favors a large, bushy, soft growth, with a 

♦Sturgis, W. C, Conn. Agr. Expt. Sta., Rept. 21: 175-181, 1898. 



Carnation Diseases 233 



consequently profuse topping, which opens the way 
to the disease. 

Control. Peltier* recommends the use of medium 
sized sturdy plants in preference to large, bushy 
ones. As much as possible, overcrowding should 
be avoided. During the first three months after the 
plants have been brought in, the temperature should 
be kept as low as the plant will tolerate. The 
syringing should never be given in the evening nor 
in the cloudy weather. It should be given on clear 
days in the morning so that the plants will be dry 
by the evening. In topping a plant, care should be 
taken to make clean cuts and to avoid leaving stubs. 
In gathering flowers, break them off at a node. 
Finally all diseased material should be pulled out 
and destroyed by fire. 

Root Rot 

Caused by Rhizoctonia solani Kuhn. 

Symptoms. The disease is at first manifested by 
a yellowing of the affected plant or branch. A few 
days later actual wilting takes place. This is true 
only in sunny weather. During cloudy weather, 
the plant remains turgescent even though the stem 
may be badly rotted. The trouble is confined to 
the stem end or to the roots of the plants. Deep 
brown lesions usually precede the rot and indicate 
the places where infection started. High tempera- 
tures and deep planting favor the disease. Of the 

♦Peltier, G. L., The Amer, Flor. 56: 725-726, 1916. 



234 Diseases of Greenhouse Crops 



older varieties, the following are reported as being 
especially susceptible to stem rot: Crimson King, 
Scott, Jubilee, La Purite, De Graws, Servan, Silver 
Spray, Flora Hill, McGowan, Portias, Boston Mar- 
ket, Craig, Lawson, Winson, and Lady Bountiful. 
The newer varieties do not seem to possess any more 
resistance than the older ones. For a description of 
the causal organism and methods of control, see p. 20. 

Root Knot 

Caused by Heterodera radicicola (Greef) Muller. 

Symptoms. Root knot is characterized by swell- 
ings of the roots. Affected plants are decidedly 
dwarfed, yellowish, and sickly looking. The roots 
of diseased plants are extensively knotted, and 
lumpy. For a description of the causal organism 
and of methods of control, see p. 28. 



CHAPTER 20 



THE CHRYSANTHEMUM {Chrysanthemum sp.) 

Cultural Considerations, Chrysanthemum cut- 
tings should be thick, firm, have several joints, and 
be about three inches in length. If the cuttings 
within three weeks fail to make a good root system, 
they should be discarded as weak stock. A house 
temperature of 50 degrees F. and a bottom heat of 
60 degrees is best suited for the cuttings. It is very 
unwise to allow the cuttings to remain in the propa- 
gating bed as soon as they start to grow. In trans- 
planting for the first time the soil should not be 
too rich. A good loam with very little rotted manure 
is all that is required by the newly rooted cuttings. 
As the plants are finally set in benches in the green- 
house (fig. 49) they need a rich soil, as they are 
heavy feeders. The benches need not be over five 
inches, the depth of the soil not over four inches. 
As the plants are first set out in the benches, it is 
advisable to water only around each plant. As they 
become well established the entire bed may be 
watered with safety. It should be borne in mind 
that the soil must be kept moist very uniformly. 
Sudden drying of the soil checks growth, and too 
much will cause the leaves to become yellow and 
sickly. On bright days, syringing the foliage is 

235 



236 Diseases of Greenhouse Crops 



very helpful. This, however, should be done in 
the early part of the day, so that the foliage will 
be dry at night. Chrysanthemums are heavy feeders, 
and this should not be lost sight of. 

Diseases of Chrysanthemums 

Chrysanthemums are subject to several important 
diseases. These often become so troublesome as to 
seriously interfere with the profitable culture of the 
plant. 

Crown Gall 

Caused by Pseudomonas tumefaciens Ew. Sm. 

This disease causes swellings on the crown and 
the roots of the plant. The trouble is seldom of any 
economic importance under greenhouse conditions. 
The causal organism attacks not only chrysanthe- 
mum, but also the daisy, geranium, sugar beet, pop- 
lar, willow, peach, etc. 

Black Speck 

Caused by Filobolus crystallinus (Wigg.) Tode. 

The speck is often found on the leaves. Some 
growers believe this specking due to the accumu- 
lation of smoke settled on the leaves after fumiga- 
tion. Others believe that it is due to a con- 
densation of ammonia arising from fresh manure. 
As stated for a similar case on roses (see p. 321 ), the 
specking is due to the discharge of sporangia of 




Fig. 50. Chrysanthemum Diseases. 

a. Botrytis blossom rot. healthy and diseased (after Spaulding-), b. ray 
blight (after Stevens. F. L.), c. chrysanthemum rust (after Smith. R. E.). d. Ure- 
dospores of Piicciniu chrysanthcmi. e. Cylindrosporium fungus, /. Cylindro- 
sporium blight {e and f after Halsted). 



Chrysanthemum Diseases 237 



Piloholus crystallinus. The spore-bearing stalks of 
this fungus are possessed with a mechanism which 
throws off the ripe spores considerable distances. 
Being covered with a sticky substance, these spore 
masses readily adhere to anything standing in the 
way. The specking may be expected wherever 
manure is used as a mulch. According to Craig* 
the trouble may be promptly stopped by a light ap- 
plication of air-slaked lime. 

Rust 

Caused by Puccinia chrysanthemi Rozc. 

Symptoms, Rust may be readily distinguished 
from all other diseases of the chrysanthemums. It 
appears as tiny, rusty blisters the size of a pinhead. 
When several appear together the blister assumes 
a larger size (fig. 50, c). At first, the blister is 
covered by the epidermis of the leaf. With age, 
however, the epidermis bursts and breaks away, ex- 
posing a brown powder which is made up of mil- 
lions of spores of the rust fungus. On badly in- 
fected plants, the leaves may be all covered with 
the rust sori which nearly always appear on the 
underside of the leaf. It was previously believed 
that the rust of chrysanthemum was the same which 
attacks common weeds belonging to the same com- 
positse family as the chrysanthemum. However, the 
investigations of Arthur t have definitely shown that 

♦Craig, J., Canada Expt. Farms Repts., 1897: 91-133, 1898. 
t Arthur, J. C, Indiana Agr. Expt. Sta. Bui. 85: 143-150, 1900. 



238 Diseases of Greenhouse Crops 



the chr}^santhemum rust attacks this plant and no 
other host. Uredospores from dandelions, burdock, 
ox-eye daisy, when sown on the chrysanthemum 
failed to produce the rust. On the other hand, ure- 
dospores taken from the chr^-santhemum and sown 
on chrv^santhemum hosts reproduce the disease. The 
disease no doubt is brought in with infected plants, 
or cuttings made from a rusted plant. 

The Organism. It is very strange that the uredo- 
spore stage (fig. 50, d) is the only stage of the 
chrysanthemum rust that is found in the United 
States. This makes the fungus short lived unless 
it is continually transmitted from living chrj'santhe- 
mum leaves to others. The uredospores are spheri- 
cal to pyriform, possessing a spiny membrane and 
three germ pores. The teleutospores were mentioned 
and figured by Massee ^ and by Roze.f However, 
without making cultures it is doubtful whether these 
claims can be accepted as final. 

Control. It is claimed that the variety Queen is 
very susceptible to rust. It is also believed that pot- 
grown plants are less resistant to rust than are plants 
growing in benches. Hand picking, selecting of 
clean, strong stock, and inside culture are recom- 
mended to keep the rust in check. The chrysanthe- 
mum rust, although serious, need not be feared by 
the careful grower who selects his stock and who is 
careful about the watering and the ventilation of 
the house. 

*Massee, G., Gard. Chron. 24: 269, 1898. 
t Roze. Bui. Soc. Myc. de France 17: 88, 1900. 



Chrysanthemum Diseases 239 
LiGULE Rot 

Caused by Sclerotinia fuckeliana (De By) Fckl. 

This rot in which the ligules become involved 
is often mistaken for a heart rot, and a destruction 
of the receptacle. The latter disease is brought 
about by nutritional disturbances. Ligule rot is 
caused by the fungus, Botrytis cinera^ the fruiting 
summer stage of Sclerotinia fuckeliana. 

Control. For ligule rot Crepin"^ recommends that 
the flower buds be sprinkled with a solution made 
up of two grams of chemically pure nitric acid to 
a liter of water. 

Blossom Rot 

Caused by Sclerotinia fuckeliana (De By) Fckl. 

Symptoms, This disease is usually confined to 
the blossoms only. The trouble first appears as 
minute discolored watery spots on the petals, giv- 
ing the latter the appearance of having been pricked 
with a needle. The white-flowered varieties show 
the spotting more distinctly than the colored ones. 
The spots rapidly enlarge and involve the entire 
corolla. Diseased petals wilt, and are soon covered 
by a grayish, velvety growth (fig. 50, a), consist- 
ing of the summer fruit (Botrytis). After the first 
few flowers become affected, the trouble spreads 

* Crepin, H., Jour. Soc. Nat. Hort. France 11:52-59, 1910. 



240 Diseases of Greenhouse Crops 



rapidly and causes great damage. According to 
Spaulding* no one variety or color of chrysanthe- 
mum showed any difference in resistance. 

Besides chrysanthemums the disease also attacks 
poinsettias (Euphorbia pulcherina). In this case 
the projecting angles on either side of the leaf be- 
come affected. It seems that with poinsettias, infec- 
tion is localized in the broad green leaves which 
grow along the stems below the red zones. At the 
place of infection there is an exudation of small 
white drops of the hardened juice along the larger 
veins. These hardened drops of juice on the dead 
spots are very characteristic of the disease on poin- 
settias. Infected leaves drop off prematurely, thus 
marring the appearance of the plant. About two 
days after infection, the characteristic fruiting of the 
fungus makes its appearance. 

Phyllosticta Leaf Spot 

Caused by Phyllosticta chrysanthemi E. and D. 

Symptoms. The spots are orbicular, purplish 
brown with a distinct border. The trouble is mostly 
confined to the leaves. 

Little is known as yet of the causal organism. It 
is probable that spraying with a standard fungicide 
will control the trouble. 

* Spaulding, P., Missouri Botanical Garden, Twenty-first Ann. 
Rept: 185-188, 1910. 



Chrysanthemum Diseases 241 



Ray Blight 

Caused by Ascochyta chrysanthemi Stevens. 

Symptoms. This disease attacks the buds or the 
opened blossoms. The affected blossom becomes 
brownish, straw colored, and withers. The discolor- 
ation nearly always begins at the base and works 
up to the tip of the blossom. Affected buds fail 
to open altogether. On opened flowers, the disease 
attacks on one side so that the rays in that direction 
will become destroyed (fig. 50, b.). The receptacle 
and the peduncle of diseased blossoms turn black and 
become shriveled. Portions of the stem may also 
be attacked, turn black and girdled. 

The Organism. Ascochyta chrysanthemi was first 
described by Stevens.* The pycnidia are few, oc- 
cur singly or scattered about, and open by means of 
a short central ostiole. The spores are oblong, 
straight or irregular, hyaline, one septate, the ends 
obtuse or acute. 

Control. All diseased material should be de- 
stroyed by fire. Careful and frequent spraying will 
control the disease. 

Septoria Leaf Spot 

Caused by Septoria chrysanthemi Cav., and S, 
chrysanthemella (Cav.) Sacc. 

Symptoms. This disease usually appears as small 

♦Stevens, F. L., Bot. Gaz. 44: 241-258, 1907, 



242 Diseases of Greenhouse Crops 



dark brown spots which increase in size until they 
meet. Affected folia<j;e drop off prematurely. Dis- 
eased plants become weakened and produce small 
flowers. The disease is oiten introduced in the 
greenhouse with infected cuttings. The pycnidia of 
the fungus are minute, while the conidia are ob- 
scurely septate. 

Control. Cuttings should be secured from healthy 
plants. All diseased leaves and trash should be de- 
stroyed by fire. Spraying with a standard fungicide 
is also recommended. 

Blight 

Caused by Cylindros [)orhiw chrysanthemi E. & D. 

Symptoms. This disease seems to work quickly 
and affected plants are short lived. The trouble 
appears on the leaves as dark blotches about one- 
half of an inch to three-quarters of an inch in 
diameter. The spore heaps are formed on the dead 
tissue where the spots occur. The area beyond the 
spot turns yellow, and soon the leaves shrivel, droop, 
and cling to the stems (fig. ^o, f.). 

77/ 6' Organism. The acervuli of this fungus are 
imbedded, the conidia are somewhat thick but taper 
to the end; they are several septate and straight (fig. 
50, e.). 

Control. Infected material should be destroyed 
by fire. Spraying with a standard fungicide will 
protect the healthy plants. 



Chrysanthciiujni Diseases 243 



Po WD r: R Y Mild k w 

Caused by Oidiutn chrysanthemi llobh. 

This is a very coiiiiiion troubh^ of indoor cbrys- 
antliemunis. Affected leaves becoiiu* covered with 
a f)owdcry white growtli. It seems tJiat the Oidiiini 
or summer stage is the only one that occurs on af- 
fected |)l:mts. The winter or ascus stag(; has not 
yet been recorded. Tlie trouble may be controlled 
in the same way as the rose mildew (see |). 323). 
Some growers f)ref(T to usct sulphur by mixing it 
with an oil and applying it to the steam pipes as a 
paint. 

CrNi.RAiUA {Cineraria crucnfa) 

Cultural Considerations. Tint culture of this 
j^lant is very simple. However, it should be kept 
in mind that it is injured by hot dry air and sensi- 
tive to slight frost. The plant should be syringed 
practically every day, winter or summer. It also 
requires a cool shaded part in the house. 

Fungi Recorded on the Cinj.raria 

The Cineraria, it seems, is very hardy. The fol- 
lowing fungi have been found on weakened or dead 
parts of the plant: Mcidiurn cineraria: Uosti, Asco- 
chyta jibricola Sacc, Coleosporium sonchi (Pers.) 
Lev., Leptospharia vagabunda Sacc., Vuccinia crio- 
phore Thum. 



244 Diseases of Greenhouse Crops 



Clematis 

Cultural Considerations same as Cyclamen, p. 
248. 

Diseases of the Clematis 

Clematis is a hardy plant. In the greenhouse it 
is subject to but few diseases. 

Anthracnose 

Caused by Glceosporium clematidis Sor. 

This disease was first met with by Sorauer * on 
Clematis Jackmanni in Germany. It is not known 
whether this disease is present in the United States. 
Its introduction into this country should be carefully 
guarded against. Little is known of the causal or- 
ganism. The disease may be kept in check by the 
destruction of diseased material. 

Leaf Spot 

Caused by Cylindrosporium clematidis E. and E. 

This trouble is manifested as reddish brown sub- 
angular to roundish spots on the leaves. The acer- 
vuli are immersed, scattered and few in numbers. 
The conidia are somewhat curved and when ripe 
exude in a white mass. C. clematidis^ var. Jack- 
manni E. and E., also found on the clematis, dif- 
fers from the former in the acervuli exuding a 

♦Sorauer P., Ztschr, Pflanzenkrank. 7: 230, 1897. 




Fig. 51. Broom Rape of Coleus (After Halsted), 



Coleus Diseases 



245 



black mass of spores which are hyaline when looked 
at individually. 

Coleus 

Cultural Considerations same as Geranium, p. 
260. 

Diseases of the Coleus 

Coleus is an unusual hardy plant in the sense that 
it is subject to so few diseases. 

Damping Off 

Caused by Rhizoctonia solani Kuhn. 

It seems that the variegated green varieties are 
more susceptible to damping off than the variegated 
red and yellow. Infected cuttings show lesions at 
the stem and above the surface of the soil. As the 
lesions spread and work in deeper in the tissue, the 
cutting topples over. For a description of the causal 
organism and methods of control, see p. 20. 

Broom Rape 

Caused by Orobanche ramosa L. 

Coleus is often subject to the attacks of a broom 
rape (fig. 51). The trouble was found by Hal- 
sted and Kelsey * on greenhouse plants. Orobanche, 
the broom rape genus, is of interest to greenhouse 
growers, because of its parasitic nature. Broom rape 

* Halsted, B. D., and Kelsey, J. A., New Jersey Agr. Expt. Sta., 
23rd Ann. Kept.: 408, 1902. 



246 Diseases of Greenhouse Crops 

is a degenerate flowering plant. According to Harsh- 
berger,* the embryo of Orobanche has no trace of 
root and stem, but it consists of a spiral filament of 
delicate cells which feeds on the stored reserved food 
of the seed. Upon coming in contact with the roots 
of a suitable host it adheres itself closely and swells 
considerably, assuming a flask-shaped appearance. 
Secondary filaments are now produced from the 
flask-shaped body which bore in and penetrate into 
the vascular system of the roots of its host, where 
it receives its food. At the point of union between 
host and parasite, a bud is formed which later de- 
velops into a thick flower bearing stem which grows 
out above ground. 

The Croton (Codiczum variegatum) 

Cultural Considerations, Care should be taken 
**^t to allow the plants to become pot bound. The 
best foliage color is obtained when exposed to full 
sunlight. The plants do well in a moist house with 
frequent syringing of the foliage. The tempera- 
ture at night should never be permitted to go down 
below 70 degrees. 

Diseases of the Croton 

The Croton is considered a very hardy plant, but 
one disease is of importance to the greenhouse man. 

* Harshberger, J. W., A text book of mycology and plant path- 
ology: 299, 1918. P. Blakiston's Son & Co., Philadelphia, Pa. 



Croton Diseases 



247 



Anthracnose 

Caused by Glceosporium soraurianum All. 

Symptoms, This disease is manifested as large 
yellowish-gray spots on the leaves, which become 
whitish, dry and brittle with age. The spots are 
more visible on the upper part, although they work 
down through the entire thickness of the leaf. The 
acervuli are usually formed within the spots and 
become apparent as salmon-colored, gelatinized dots. 
The causal organism resembles other Glceosporium 
in structure. G. soraurianum is probably the same 
as G. crotonis Del., also found to attack croton 
leaves. 

CoRDYLiNE {Cordyline aus traits) 

Cultural Considerations, This plant greatly re- 
sembles dracenas. Cordylines are usually grown in 
pots. They require a warm moist atmosphere, and 
are sensitive to full light. However, during the 
fall they should be kept drier, and exposed to full 
light in order to better bring out the color of the 
foliage. 

Fungi Recorded on the Cordyline 

The plant is apparently very hardy. The follow- 
ing fungi have been recorded : Colletotrichum cordy- 
lines Polla., Macrophoma cordylines (Thum.) Berl. 
and Vogl., Phyllachora vervisegiua West., Fhyllos- 
ticta cordylines Sacc. and Berl. 



CHAPTER 21 



CYCLAMEN {Cyclameti persicurnj^ 

Cultural Considerations. Greenhouse men prefer 
to sow the cyclamen seed in September and not in 
spring. In March, the seedlings are transplanted 
from a two-inch to a four-inch pot and put in a 
cold frame until large enough to go to a six-inch pot. 
During the summer, plenty of ventilation and shad- 
ing should be provided and the plants frequently 
syringed. In the fall, they are brought into the 
greenhouse (fig. 52) and some heat provided. The 
winter temperature should average 55 to 60 degrees 
F. until the period of blossoming is over. As the 
leaves turn yellow, the pots are placed in a cool 
house, water withheld and the period of rest in- 
duced. However, a little water is given from time 
to time to prevent the bulbs from shriveling. 

Diseases of the Cyclamen 
Cyclamen are subject to but few serious diseases. 

Root Rot 

Caused by Thielavia hasicola Zopf. 

The disease was reported by Sorauer * as being 

♦Sorauer, P., Ztschr. Pfianzenkrank. 6: 18, 1895. 

248 



Cyclamen Diseases 249 



serious in Germany. The general symptoms are the 
same as for the violets. For a description of the 
causal organism and general methods of control, see 

p. 355- 

Leaf Spot 

Caused by Glomerella rufomaculans^ var. cycla- 
minis Patt. and Ch. 

Symptoms, The spots are circular, watersoaked, 
with sharply defined borders. 

The Organism. The acervuli of the causal organ- 
ism are brownish, large, conidia straight to slightly 
curved. Setse are few, short and rigid. It is very 
probable that this conidial stage is the same as that 
described by Halsted as Colletotrichum cyclamencz 
Hals. The ascus stage was found by Patterson and 
Charles.* The perithecia are dense, found in defi- 
nite light colored round spots, brown membrana- 
ceous, subglobose with distinct opening. The asci 
are eight spored, the spores are hyaline, one celled, 
oblong to elliptic. The methods of control would 
be the same as for Colletotrichum cyclamena, 

Anthracnose 

Caused by ColL 'otrichum cyclamens Hals. 

Symptoms, Anthracnose produces spots (fig. 52) 
on the leaves which may be mistaken for the spots 
caused by Fhoma cyclamencz. Infection may occur 

♦Patterson, F. W., and Charles, V. K., U. S. Dept. of Agr. Bur. 
PI, Ind. Bui. 171:12-13, 1910. 



250 Diseases of Greenhouse Crops 



at any part of the leaf and spread in all directions. 
Cyclamen leaves are especially receptive to infec- 
tion because of the fact that water is able to lodge 
and remain a long time. 

Leaf Spot 

Caused by Phoma cyclamencz Hals. 

Symptoms, The disease attacks leaves of all ages. 
The affected portions become darkened. Later the 
spots become dry and lighter in color, made up of 
a series of concentric rings of light and dark bands. 
The dead spots become brittle and drop out at the 
least touch, giving the appearance of a shot hole. 
This trouble is different from the leaf spot caused 
by the Septoria cyclaminis Dur. and M. The causal 
organisms of both of these leaf spots are little 
known. 

Control, Removing the affected leaves and spray- 
ing with a standard fungicide will materially assist 
in keeping the disease in check. 

Drag EN AS {Dracena fragans) 

Cultural Considerations, The cultural require- 
ments of Dracena are the same as for Cordyline, 
see p. 247. 

Diseases of Dracenas 

Dracenas are usually considered a hardy plant. 
However, they are subject to a few but serious 
diseases. 



Fig. 53. Dracexa Diseases. 

a. Dracena tip blight, b. Pli^'llosticta 
leaf spot (both after Halsted). 



Dracenas Diseases 251 



Leaf Spot and Tip Blight 

Caused by Fhysalospora dracence Sheld. 

The conidial stage as first mentioned by Halsted 
is a species of Gloeosporium. However, the ascus 
stage was found by Sheldon,* who named it Fhysa- 
lospora dracencz. The disease is generally confined 
to the tip of the foliage (fig. 53, a.). The affected 
tissue becomes straw colored and shrunken. The 
disease may be controlled by spraying with a stand- 
ard fungicide. 

Phyllosticta Leaf Spot 

Caused by Phyllosticta maculicola Hals. 

Dracenae, particularly the beautiful species 
Cordyline terminales^ are often subject to a leaf 
spot which renders them worthless. The disease 
attacks plants of all ages and sizes. 

Symptoms, The trouble is characterized by small, 
brown, somewhat angular spots on the leaves (fig. 
53, b.). The tissue adjoining the spots becomes 
yellowish in color. Within these spots may be 
found minute black bodies (pycnidia) from which 
the spores, when ripe, ooze out as long colorless 
tendrils. Little is known of the organism. The 
disease may be controlled by spraying. 
*Sheldon, J. L., Jour. Myc. 13: 138-140, 1907. 



252 Diseases of Greenhouse Crops 



Leaf Spot 

Caused by Phyllosticta drac(zncz Griff, and Maubl. 

Symptoms, This trouble is manifested as minute, 
irregular pale spots and bordered by a narrow, 
brown colored elevated band. The pycnidia are 
not always present on the spots until the leaves 
fall off. The spores ooze out as whitish tendrils. 
This form of spot was first described by Griffon 
and Maublanc * on greenhouse dracense in France. 
Its extent in the United States is as yet little known. 

Leaf Blotch 

Caused by V ermicularia concentrica Sev. 

The thicker-leaved sorts such as Dracena goldiena 
and the variegated D. Lindemi are often subject 
to a blotch disease. The trouble is characterized by 
large, brown blotches on the leaves. Very little 
is known of the causal organism. Spraying with 
Bordeaux or any other colorless fungicide may con- 
trol the disease. 

Daffodils 
Cultural Considerations^ see Tulips, p. 348. 

Diseases of the Daffodil 

The Daffodil is a very hardy plant. It thrives 
equally as well in the greenhouse as it does out of 
doors. 

* GriflFon, M. M., and Maublanc, Bui. Soc. Mycol. de France 25 : 
239, 1 9 10. 



Daffodil Diseases 253 



Yellow Stripe 

Cause, improper cultural conditions. 

Symptoms. Yellow stripe is a disease which is 
more commonly met with under field conditions, 
but also appears on daffodils under glass. The 
trouble in its early stage is perceptible as a slight 
discoloration, or a yellowing of the veins of the 
leaves. In an advanced stage, the leaves become 
streaked with parallel bands of yellow. In ex- 
treme cases, the leaves wither and the plants fail 
to set blossoms. The disease was studied by Dar- 
lington,* who decided that the cause of it is not 
a parasitic organism, but that it is due to some uut 
favorable cultural conditions that are as yet unde- 
termined. No methods of control are known. 

Erica {Erica spp,) 

Cultural Considerations. Ericas are low growing 
evergreen shrubs which lend themselves admirably 
to forcing on a commercial scale. Too much or 
too little water is injurious to the plant especially 
during the blooming period. The plants should 
never be allowed to wilt. The pots shoifld be reno- 
vated every year individually and the proper amount 
of water given. The plants also need all the ven- 
tilation possible. 

* Darlington, H. R., Jour. Roy. Hort. Soc. (London) 34:161-166, 
1908. 



254 Diseases of Greenhouse Crops 



Fungi on the Ericas 

Ericas are apparently very hardy plants. The 
only fungus known to cause a disease on greenhouse 
plants is Stemphylium ericoctomim Br. and De By. 
The other recorded fungi are as follows : Cystospora 
ericeti Sacc, Sporonema ohturatum (Fr.) Sacc, 
Trichosporium fuUginosum Karst. 

Ferns 

Cultural Considerations, Ferns are propagated 
by spores, or by division of the clumps. The spores 
are sown on garden loam over which half an inch of 
fine sphagnum has been placed. The spores are 
scattered evenly, and after being sprinkled with 
water are covered with a glass. In the division of 
the crowns, they should be planted and kept in a 
cool house or frame until they make a good start. 
Most greenhouse ferns thrive best in a temperature 
of 60 to 65 degrees F. 

The following ferns are usually grown on a com- 
mercial scale : Adianthum cuneatum and A. gracilli- 
num. Adianthum farleyense seems among the best 
for decorative purposes. Pteris serrulata is also ex- 
tensively grown. In large conservatories the tree 
ferns, especially Alsophila australis, is very much 
in favor. Of the ferns propagated and sold for 
dwelling house purposes may be mentioned the sword 
fern, Nephrolepis exaltata. The latter can stand 
the atmosphere of a dry room better than any other 
fern. 



Fern Diseases 255 



Diseases of the Fern 

Ferns as a rule are hardy plants when they are 
given reasonable care. They are, however, attacked 
by a few diseases which are of economic importance. 

Tip Burn 
Cause, physiological. 

Ornamental ferns grown in greenhouse or in bay 
windows are often troubled by a tip burn of the 
foliage. This is generally confined to the tender 
new growth. Affected leaflets become brown at 
the tip, giving the entire leaf an unsightly appear- 
ance. There may be various causes responsible for 
this trouble. An insufficient water supply at the 
roots will cause the tender leaflets to wilt. If the 
soil is allowed to remain dry for any length of time, 
the wilted parts will dry out and become brown. 
Poisonous gases either from smoke or fumigation 
will also cause the tender leaflets to dry up and 
die, thus giving them a burned appearance. Ex- 
tremes of heat or cold will have a similar effect on 
the tender tips of the foliage. 

Control. It is evident that in this case removing 
the cause of the trouble will effect a cure. 

Leaf Scorch 
Cause, physiological. 

Symptoms, The trouble appears as prominent 



256 Diseases of Greenhouse Crops 

wedge shaped, reddish-brown spots extending in- 
wards from the cleft of the pinnse. Affected plants 
take on a variegated appearance and are less luxuri- 
ant, but otherwise seem healthy. According to Clin- 
ton* the scorching may not necessarily be the effect 
of burning by the sun's rays. It seems, nevertheless, 
due to the loss of moisture from drought caused by 
poor watering or to sudden changes of humidity in 
the air. The fern Adiantum farleyense is very deli- 
cate, and its thin leaves are more sensitive to un- 
favorable conditions. 

Yellows 

Caused by overwatering or too much nitrogen in 
the soil. 

Symptoms, Diseased plants lose their green color 
and turn white. Growth ceases and all leaflets even- 
tually drop off (fig. 54). 

Control. In repotting the plant into new soil it 
outgrows the disease. 

Damping Off 

Caused by Fythium interiiiedium De By. 

This disease attacks young fern prothallia. The 
latter turn soft, limp, and darker in color than 
the healthy ones. In general structure the organism 
resembles Fythium de Baryanum, It differs, how- 

* Clinton, G. P., Connecticut Agr. Expt. Sta., 31st and 32nd Ann. 
Kept.: 349-350, 1908. 



Fig. 55. Fern Diseases. 

a. Host cell invaded with resting spores o£ Completoria complens, b. hos^ 
cell with fungus body of C. complens, central cell forming resting spores, 
and some of the peripheral ones developing conidia, d. fungus body in host, 
the peripheral cells of which develop tubes which penetrate adjacent cells 
of fern prothallium, d. two young plants in one cell of the host, having en- 
tered from an adjacent cell {a-d after Atkinson). 



Fern Diseases 257 



ever, with regard to the zoospores. As worked out 
by Atkinson* the zoospores in P. intermedius are 
broadly fusoid, with pointed ends, and terminating 
at each end in a long cilium. After moving about 
for five to ten minutes, it gradually comes to a rest, 
the body undergoing plastic movement until the 
organism is cut into two parts, forming now two 
zoospores oval in form and each with a cilium at- 
tached directly at the smaller end. This peculiarity- 
makes this organism different from Pythium de 
Baryanum, For control method soil sterilization is* 
recommended (see pp. 32-43). 

COMPLETORIA DAMPING OfF 

Caused by Completoria com pi ens Lohde. 

Symptoms. The disease attacks young fern pro- 
thaliia. It is manifested as a yellowish or yellowish- 
brown color of the prothallia as they lay on the soil 
in the bed or pot. A careful examination will show 
that the prothallia are spotted, the spots varying 
from yellowish-green to yellowish-brown, changing 
to deep brown and to black. In an advanced stage, 
a prothallium will present a checkered or mosaic 
appearance. As rot sets in, the prothallium becomes 
ragged and torn. 

The Organism. The causal organism was studied 
by Atkinson.! The mycelium of the fungus is made 

♦Atkinson, G. F., New York (Cornell) Agr. Expt. Sta. Bui. 94: 
347-250, 1895. 

t Ibid., 252-260, 1895. 



258 Diseases of Greenhouse Crops 

up of compact clusters of oval or curved branches 
originating from a common center. This vegetative 
body occupies a single cell of the affected prothallium, 
later putting out a slender germ tube which pierces 
the adjoining intervening wall, forming clusters of 
oval mycelial branches which become rounded and 
play the part of resting spores. Each of them may 
germinate by sending out a short germ tube at the 
tip of which a conidium is formed. When mature, 
the latter breaks off and is capable of germinating. 
Upon coming in contact with the host the conidia 
germinate by sending out a flask-shaped tube which 
comes close to the wall of a cell. The protoplasm 
of the conidium now migrates into the inflated germ 
tube. The latter produces a slender tube which 
bores its way into the cell of the prothallium, where 
it swells and grows in a fashion previously described 
(fig. 55, a to d.). Completoria complens attacks 
prothallia of the following ferns: Aspidium (Cyro- 
tominum) falcatum, Pterisargyria, and Pt. cretica. 
Very little is as yet known of its method of control. 

Phyllosticta Leaf Spot 

Caused by Phyllosticta pteridis Hals. 

Symptoms. Ornamental ferns, such as Pteris 
cretica var. Magnifica are especially susceptible. The 
first symptoms of the spot disease is loss of the nor- 
mal green in the frond. This is soon followed by the 
appearance of the ashy-gray spots surrounded by a 
border that is either purple or brown. Within the 



Fern Diseases 



259 



spot are found minute black pimples, which are 
really the pycnidia or fruiting sacs of the fungus. 

The Organism. Fhyllosticta pteridis was first de- 
scribed by Halsted"^ in 1893. Since that time the 
fungus has received no further attention from plant 
pathologists, hence little is known of its life history. 
It is probable that spraying with Bordeaux mixture 
will protect the healthy foliage. 

AtuGM Parasites on Ferns 

Caused by species of Oscillatoria. 

In damp houses and overwatered soils, the pro- 
thalia of ferns are often overrun by certain algae 
which chokes them. This is accomplished by shut- 
ting out the air and light, interfering with their 
development and causing them to be completely 
sterile. As a result, many of the prothalia die. 
As a control measure, soil sterilization is recom- 
mended, see pp. 32-43. 

Gardenia {Gardenia jasminoidesy, 

Cultural Considerations, Gardenias are very sen- 
sitive and easily injured if the temperature falls too 
low during cold nights. By the end of August, it is 
advisable to maintain some heat at night so that; 
the temperature may be maintained at about 65 
degrees F. The plants require an abundance of 
ventilation. However, the ventilators should be 

♦Halsted, B. D., New Jersey Agr. Expt. Sta., Fourteenth Ann. 
Rept.: 420-421, 1893. 



26o Diseases of Greenhouse Crops 



opened gradually in the morning and closed like- 
wise towards the evening. During cloudy days of 
November and December, care should be taken not 
to overfeed the plants with liquid manure. 

Fungi on Gardenias 

Gardenias are apparently very hardy plants. The 
following are the recorded fungi: Fumago vagans 
Pers., Hemileia vastatrix B. and Br., Hypocrella 
gardeniiz Henn., and Sphcerella gardeni(Z Cke. 

Genist^e {Cystisus racemosus canariensis) 

Cultural Considerations, In the fall, the plants 
are started at a low temperature of about 55 de- 
grees F. The plants are easy to grow and require 
no special care if proper attention is given to the 
ventilation and watering. 

Diseases of Genist^e 

Genistas are very hardy plants. There is but one 
disease recorded by Kirchner* on greenhouse plants. 
The causal fungus is Ceratophorum setosum Kirch., 
which causes a disease on leaves and young shoots of 
Cytisus. 

Geranium {Geranium sp.) 

Cultural Considerations, Geraniums are mostly 
grown as a pot plant to be sold for house or out- 

♦Kirchner, O., Zeit. Pflanzenkrank., 2:324, 1892. 



Fig 56. Geranium Diseases. 

a. Dropsy, b. broom rape (a and b after Halsted), c. bacterial _ rot (after 
Galloway), d-e. bacterial spot, f. colonies of Pseudomonas erodii (d to f 
after Lewis). 



Geranium Diseases 261 



of-doors purposes. Geraniums are easily grown. 
All they need is a soil fairly rich and an abundance 
of ventilation. It needs plenty of water, but will 
rot when overwatered. This is especially true for 
the cutting bed. 

Diseases of the Geranium 

The geranium, although a hardy plant, is sub- 
ject to the attacks of several important diseases. 

Dropsy 
Cause, physiological. 

Symptoms, Dropsy is a serious trouble which is 
confined to the leaves (fig. 56, a) and petioles and 
blades. Upon the stems and petioles, it appears as 
peculiar corky ridges. On the blades, it appears as 
numerous watersoaked specks of a clear amber color 
when held up to the light. The disease may attack 
all the plants in the greenhouse. In this case, the 
older foliage shows best the watersoaked specks. 
Such leaves soon lose their normal green color, at 
first turning yellow in spots, then throughout. In 
extreme cases, although the affected plant forms the 
normal number of leaves, they remain dwarfed and 
puny, and are badly specked before unfolding. 
Plants spotted lightly often recover when removed 
out of doors. The disease is worst in the early 
spring, when it attacks, mostly, young potted gera- 
niums. As a rule, the blotches and pimples are quite 



262 Diseases of Greenhouse Crops 



evenly distributed. The specks, however, differ in 
form. Some are very irregular in outline while 
others are almost circular. 

Cause. Dropsy is favored by poor light, wet soil, 
and a high soil temperature. Dropsy may be looked 
for in late winter with long nights, short days and 
cloudy weather. This causes an excessive root ac- 
tion with results injurious to the plant. 

Control, Dropsy may be controlled by providing 
a cooler, dryer soil, and by exposing the plants to 
the direction where they will receive the greatest 
amount of light and ventilation. 

Leaf Spot 

Caused by Fseudomonas erodii Lewis. 

Symptoms, This disease was found by Lewis * 
on greenhouse geraniums in Texas. It is not known 
how serious or how extensive the disease may ap- 
pear to be in different parts of the country. It is to 
be assumed that it is more or less prevalent in every 
greenhouse where it has been spread about by infect- 
ed plants or cuttings. 

The disease attacks four varieties of ornamental 
geraniums and the symptoms are the same on all. 
On the leaves, the spots first appear as minute dots 
which are transparent through light. With age the 
spots enlarge, become reddish brown in the center 
with ^a colorless border, resembling much the frog 
eye spot of the apple (fig. 56, d and e.). There 

* Lewis, I. M., Phytopath, 4:221-231, 1914. 



Geranium Diseases 263 



is also a tendency to form large spots between the 
principal veins. In this case, however, infection be- 
gins at the margin of the leaf and progresses in- 
wards. Spotted leaves may also become pale and 
drop off prematurely. 

The Organism. Fseudomonas erodii is a short 
but rather plump rod with rounded ends, borne 
singly or in short chains of 2 to 3, active by means 
of polar flagella. It produces no spores, and lique- 
fies gelatin. 

Control. There seems no evidence that insects 
are in any way associated with the spread of the 
disease in the greenhouse. The causal organism 
lives in the soil and is spread about by the splashing 
of water during watering. By the removal of the 
diseased parts and by careful attention to the water- 
ing, the disease may be kept in check. The same 
disease also attacks the wild geranium, Erodium 
Texanum, which in this case may act as a carrier of 
the causal organism. This weed therefore should 
not be tolerated around greenhouses where gerani- 
ums are grown, nor should it be used in the compost 
soil. 

Soft Rot 

Caused by Bacillus caulivorus Pr. and Del. 

Symptoms. This disease was found by Gallo- 
way * to be destructive to greenhouse geraniums. 
It attacks the stems which at first become soft and 
mushy and later turn black and shrivel (fig. 56, c). 

*GaIloway, B. T., Jour. Mycol. 6; 114-115, 1890. 



264 Diseases of Greenhouse Crops 



Cuttings are especially susceptible and rotting usu- 
ally starts at the cut and works upward, destroying 
it entirely. Rooted cuttings are not as likely to be- 
come infected as those freshly made and planted. 
The disease is most prevalent where young imma- 
ture cuttings are made, and where the soil has been 
excessively damp and the house poorly ventilated. 
Little is known of the causal organism. 

Damping Off 

Caused by Pythium de Baryanum Hesse. 

This disease confines its attacks mainly to gera- 
nium cuttings. For a description of the causal or- 
ganism and of methods of control, see p. 17. 

Gray Mold 

Caused by Sclerotinia fuckeliana (De By.) Fckl. 

Symptoms, Gray mold is manifested as dead 
brown spots on the leaves. Under moisture condi- 
tions, the gray moldy growth appears. This is but 
the Botrytis or summer fruiting stage of the fungus. 
The trouble is prevalent in leaky houses or where 
water is used in excess and the beds are poorly 
drained. By proper ventilation, and by careful 
watering the mold may be kept in check. 

Leaf Spot 

Caused by Coniothyrium trahuti Riza. 

As far as is known this disease is not known to 



Geranium Diseases 265 



occur in the United States. It was first recorded 
by Ali Riza * as attacking geranium leaves, causing 
them to dry and shrivel. 

Broom Rape 

Caused by Orobanche minor J. Esm. 

This parasite is frequently met with on clover in 
the fields. Its attack on greenhouse geraniums was 
first reported by Halsted.f The seeds of this para- 
site germinate in the soil. Soon after its roots be- 
come attached to those of the geraniums. The 
growth of the broom rape is soon apparent as a pur- 
plish, erect stem with scale-like purplish leaves above 
the ground. Later a number of blossoms are formed 
along the unbranched stem. The attacked geranium 
becomes sickly in appearance (fig. 56, b.). Steam 
sterilization of the soil will kill the seed of broom 
rape. 

* AH Riza, Bui. Trimest. Soc. Mycol. France, 28: 148-150, 1912. 
t Halsted, B. D., et al,, New Jersey Agr. Expt. Sta., Twenty- 
sixth Ann. Kept.: 509, 1905. 



CHAPTER 22 



HYACINTH {Hyacinthus orientalist 

Cultural Considerations, In forcing (fig. 57, a) 
hyacinths it is important that they start with a well 
developed root system. Otherwise the culture is the 
same as for narcissus (see p. 287). 

Diseases of the Hyacinth 

The few diseases which hyacinths are subject to 
are serious. Most of these, no doubt, have been 
brought in with imported bulbs. 

GuMOSIS 

Cause, physiological. 

Symptoms, This trouble is characterized by the 
formation of pure white gum pockets between the 
epidermis and lower tissue. In this case the starch 
apparently becomes replaced by gum through a proc- 
ess of degeneration. The gum bearing cells often 
enlarge abnormally. The true cause of this trouble 
is unknown, but it is generally attributed to im- 
proper culture. 

266 




a. Tj-pe of bulb house, h-h. hjacinth 3-ellows, showing type of injury to 
bulbs, leaves, and blossoms, i. Pseudonionas hyacinthi (b-i after Smith, E. F.). 



Hyacinth Diseases 267 



Soft White Rot 

Caused by Bacillus hyacinthi septicus Heinz. 

This disease has been studied by Heinz.* Its 
presence in this country is unknown. Affected bulbs 
become soft rotted but remain white. 

Yellows 

Caused by Pseudomonas hyacinthi (Wak.) Sm. 

Symptoms. This disease as described by Smith f 
and others is characterized as follows : Early infec- 
tion becomes apparent as water soaked stripes, soon 
followed by a yellowing then browning and dying 
of the affected tissue. The water soaked stripes soon 
spread all over the foliage, and the accompanying 
symptoms are the same as previously mentioned. 
The stripes usually start at the apex of the leaves. 
Frequently, the stripe runs down the entire length 
of the foliage while both margins remain green. On 
the flower stalks the disease is also manifested as a 
water soaked spot followed by the characteristic 
browning and shriveling. Infection on the bulb is at 
first confined to the vascular bundles the latter of 
which become yellow and gorged with slime. The 
disease soon spreads, invading and destroying the 
scales, the latter becoming yellow and soggy. Nu- 
merous other invading organisms often enter and 

♦Heinz, Cent. f. Bakt. 5: 535, 1889. 

t Smith, E. F., Bacteria in Relation to Plant Diseases, 2:335-353, 
1911. 



268 Diseases of Greenhouse Crops 



help to complete the decay and the disorganization 
of the bulb. Often bulbs are attacked on one side 
only, in which case the growth of the foliage is also 
one sided, curved, and bends over towards the dis- 
eased side (fig. 57, b to h.). 

The Organism, Pseudomonas hyacinthi is a me- 
dium sized rod, rounded at both ends, and is actively 
motile by means of one long polar flagellum (fig. 
57, i.). It is non-sporiferous, produces no gas, and 
liquefies gelatin slowly. 

Control, It is fortunate that the disease has not 
as yet proved serious in the United States. It is a 
very important disease in the Netherlands, and its 
introduction with imported bulbs should be guarded 
against by growers in th^ United States. 

It is very fortunate that there exists a considerable 
difference of resistance to yellows among hyacinth 
varieties, as seen by the following list : 



RESISTANT 



NON-RESISTANT 



Single Red 



Robert Steiger 

Gertrude 

Homerus 



Single Rose 



Charles Dickens 



Baroness v. Tuyll 
Moreno 



Single White 



Grandeur a Merveille 
La Franchise 



La Grandesse 
La Neige 



Single Light Blue 



Captain Boyton 
Czar Peter 
Grand Lilas 
Leonidas 
Lord Derby 
Lord Palmerston 
Orandates 
Queen of Blues 
Schotel 



Grand Maitre 
La Peyrouse 
Regulus 



Hyacinth Diseases 269 



RESISTANT NON-RESISTANT 

Single Dark Blue 
King of the Blues Argus 

General Havelock 
King of the Blacks 
Masterpiece 
Mimosa 
Single Yellow and Orange 
King of the Yellows Bird of Paradise 

Yellow Hammer Hermann 

Ida 

La citromere 
L'or d'Australie 



Double Red 
Double Rose 



Princesse Royale 
Bouquet Royal 

Double White 

Flevo Florence Nightingale 

La Virginity Grand Vain Queen 

La Tour d'Auvergne 
Double Dark Blue 
Crown Prince of Sweden 

In Holland the disease is kept in check by the de- 
struction of diseased plants. Diseased bulbs should 
never be planted since they will surely introduce 
the disease in new localities. Spraying in this case 
will be of no benefit. 



Damping Off 

Caused by Dictyuchus monosporus Seitg. 

Symptoms, The above fungus causes a serious 
damping off, the symptoms of which resemble those 
of other plants. Dictyuchus monosporus is the only 
one of the genus Saprolginiacese which is reported 
by Halsted as being parasitic on plants. 

The Organism, The sporangia are clavate. The 
swarm spores become walled within the sporangium 



270 Diseases of Greenhouse Crops 



and emerge singly through its lateral walls. For 
methods of control soil sterilization is recommended 
(see pp. 32-43). 

Bulb Rot 

Caused by Rosellinia massinhii Sacc. 

This fungus is reported by Halsted as thriving 
on hyacinth bulbs. However, the nature of the in- 
jury is not clearly stated by him. 

The Organism. The fungus produces dark brown, 
elliptical spores. The asci are borne in globose or 
depressed dark colored perithecia. 

SCLEROTINIA ROT 

Caused by Sclerotinia bulborum Rehn. 

Symptoms. The disease is first manifested as yel- 
low stripes or blotches on the leaves and bulbs. With 
the advance of the trouble, a velvety olive brown 
mold is formed on the surface of the spots. This 
growth is but the conidiophores and conidia of the 
causal fungus. The black sclerotia are developed 
on the rotted bulbs, and are found mostly within 
the outer scales. As the sclerotia winter over, 
they germinate by sending out slender stalks which 
bear apothecia and ascospores. The Botrytis form 
of spores is the most prevalent and is depended 
upon by the fungus to spread it quickly from plant 
to plant. 

♦Halsted, B. D., N. J. Agr. Expt. Sta., Fourteenth Ann, Rept 
393, 1893. 



Hyacinth Diseases 271 



Control. Since numerous sclerotia are left in the 
soil with decayed bulbs, steam sterilization of the 
soil is recommended. Badly infected bulbs should 
be removed and destroyed by fire. Plenty of ven- 
tilation should be provided whenever possible. 

Nematode 

Caused by Tylenchus dipsaci Kuhn. 

Symptoms. This disease was first found in the 
United States by Byars * on imported hyacinth 
bulbs. It is prevalent in Europe where it attacks 
besides the hyacinth, clover, alfalfa, rye, oats, onion, 
potatoes, and numerous other wild and cultivated 
plants. 

On the leaves, the nematode produces character- 
istic distortions and yellow to brown longitudinal 
discolorations. At the end of the growing season, 
the parasite migrates from the leaves to the scales 
of the bulbs. Diseased scales become discolored, so 
that when one cuts through an infected bulb, one or 
more yellow characteristic rings become very appar- 
ent. 

The Organism. The adult worm is barely per- 
ceptible to the naked eye. It may, however, be read- 
ily seen with a magnifying hand lens. Each female 
produces numerous eggs which hatch into larvge, the 
latter of which reach maturity quickly. This means 
that several generations are produced in one season. 

Control. The disease is carried with infected 

♦Byars, L. P., Phytopath. 4:45, 1914. 



272 Diseases of Greenhouse Crops 



bulbs. The latter should therefore be discarded and 
only healthy ones used. 

Grape Hyacinth {Muscari hotryoides) 

Cultural Considerations, As soon as the bulbs are 
brought in the house, they should be given the bene- 
fit of the full light, and a low temperature. Neg- 
lect in this direction will result in spindly weak 
plants. 

Fungi of the Grape Hyacinth 

This plant is apparently very hardy. There are 
but two fungi recorded on this host : 

Uromyces scillarum (Grev.) Wint., Ustilago 
vaillantii Tul. 

Hydrangea {Hydrangea kortensis) 

Cultural Considerations, Hydrangeas are valu- 
able because of their adaptability to forcing for the 
Easter trade. Plants should be brought in the early 
part of January and freed from all old and dead 
leaves. The beginning temperature should be about 
45 degrees F. and after two weeks it should be raised 
ten more degrees. To force them to flower the tem- 
perature is raised to degrees. Ten days before 
Easter the blooming plants are given a temperature 
of 50 to 55 degrees. This hardens the blossoms and 
gives them better keeping qualities. During active 
growth they need plenty of ventilation, sunlight, 
and water, and frequent syringing. 



Hydrangea Diseases 273 



Diseases of Hydrangeas 

Hydrangeas are very hardy plants. They are sub- 
ject to but few diseases, which are of little impor- 
tance. 

Rust of Hydrangea 

Caused by Fucciniastrum hydrangea (B. and C.) 
Arth. 

Rust is a serious disease on hydrangeas. The ure- 
dinial and tetial stages of the causal organism are do- 
ing the damage. Selby ^ was perhaps the first to 
have observed the rust, although little more has been 
added to our knowledge of it or of methods of con- 
trol. 

The Organism. As far as is known Fucciniastrum 
hydrangea has only two spore stages, the uredo and 
teliospores. The uredinia are found scattered most- 
ly on the under side of the leaf, their color dark 
yellow to pale yellow. The peridium is delicate, the 
cells are small, while the walls are thin throughout. 
The ostiolar cells are somewhat elongated, and 
slightly pointed, the spores are broadly elliptical to 
ovate; the cell wall is thin and warty. The telia are 
usually found on the lower part of the leaf in small 
angular groups, that are rather flat and reddish 
brown in color. Spores are formed in a single layer 
within the epidermal cells or immediately beneath 
it ; the cell wall is thin, and a dark, cinnamon brown 
in color. No methods of control are known. The 

♦Selby, A. D., Ohio Agr. Expt Sta., Bui. 214: 402, 1910. 



274 Diseases of Greenhouse Crops 



disease may be introduced into the greenhouse with 
infected plants. 

Leaf Spot 

Caused by Phyllosticta Jiydrangecz E. and E. 

The disease is characterized by large, rusty, brown 
spots occurring on the leaves, especially at the edges. 
The disease is often so severe that it is necessary to 
cut off the top of the plant. Upon examination of 
the affected leaves, numerous minute, black pycnidia 
will be found scattered throughout. The conidia are 
oblong, hyaline, and one celled, and generally ooze 
out as minute creamy tendrils. The disease may be 
kept in check by spraying with a standard fungicide. 



CHAPTER 23 



LILAC {Syringia vulgaris) 

Cultural Considerations, Indoor lilacs at first re- 
quire a cool house. The temperature is gradually in- 
creased to about 60 degrees. The plants require fre- 
quent syringing and moderate ventilation. 

Diseases of the Lilac 

Forced lilacs are subject to a few diseases. The 
plant is generally considered very hardy. 

Leaf Blight 

Caused by Pseudomonas syring<2 van. Hall. 

Symptoms, The disease as described by Gussow * 
seems to be confined to the leaves. The writer has 
found a blossom blight of the lilac both indoors and 
in the field. In pure culture, the organism resem- 
bled P. syringcz. The affected leaves become greatly 
disfigured; the disease spreads very rapidly. 

Control, It is doubtful whether spraying will be 
of any avail. The plants should be given plenty 
of ventilation whenever possible. Diseased leaves 
should be destroyed by fire. As far as possible the 

•Gussow, H. T., Gard. Chron. 44: 404-405, 1908. 

275 



276 Diseases of Greenhouse Crops 



leaves of the plants should be kept dry; all the water 
should be applied with the hose on the ground, a 
method that also avoids the splashing of soil par- 
ticles. 

Twig Blight 

Caused by Fhytophthora syringa Kleb. 

This disease was found by Klebahn ^ to be very 
serious in propagating beds in Germany. The causal 
organism attacks and kills the twigs at a distance 
of several internodes above ground. The flower 
buds from the affected shoots fail to develop alto- 
gether. However, new shoots may appear below the 
affected area. The disease is of no economic sig- 
nificance in the United States. 

Powdery Mildew 

Q2MS>td hy Micro sphczr a alni (Wal.) Salm. 

Symptoms. Powdery mildew is perhaps one of 
the commonest troubles of forced lilacs. The dis- 
ease is characterized by white powdery patches on 
the surface of the leaves and stems of the plant. The 
causal fungus attacks a large number of outdoor 
plants besides the lilac, as chief of which Lonicera, 
Alnus, Betula, Quercus, Carya, Castanea, Juglans, 
and Platanus may be mentioned. Outdoor lilac 
often suffers greatly from this mildew. 

The Organism, The perithecia are either scat- 

* Klebahn, H., Krankheiten des Fielders (Berlin) 175, 1909. 



Lilac Diseases 



277 



tered or crowded greatly, varying in size. This 
seems also true for the appendages, which vary in 
length and in numbers, but are rigid, and colorless 
throughout, excepting the amber brown base, and 
dichotomously branched at the tips, the latter 
branches being regularly recurved. The asci are 
short stalked, ovate to globose ; the ascospores are 8 
in number. 

Control. This mildew may be controlled in the 
same way as the rose mildew (see p. 323). 

Lilies (Lilium longi'florum) 

Cultural Considerations, The secret of success 
with lilies is in strong and vigorous bulbs. Lilies 
forced for the Christmas market should be planted 
in a rich soil thoroughly mixed with well rotted 
stable manure. After having been potted, the bulbs 
should be placed in a cold frame or in a cool dark 
cellar to encourage the rapid rooting. After that 
they are maintained at a temperature of 50, then 
60, then 75 degrees F. in the house. Lilies for the 
Easter trade are bought about the middle of Decem- 
ber. Lilium speciosum var. rubrum is especially 
well adapted for forcing. 

Diseases of Lilies 

Lilies are subject to quite a number of diseases all 
of which are of economic importance. 



278 Diseases of Greenhouse Crops 



The Bermuda Disease 
Cause, cultural and mites, 

Symptoms, The trouble is characterized by a 
spotting and distortion of the leaves, flowers, and 
scales of the bulbs, as well as by a general stunting 
in growth. In severe cases, there appear yellowish 
white, longitudinal, sunken spots, and streaks on the 
first leaves as they show above ground. As growth 
proceeds each succeeding whorl becomes similarly 
affected, and finally collapses and dries. Even the 
flowers become spotted, shrunken, and distorted. 
Occasionally plants appear healthy, until the disease 
suddenly breaks out on the flowers. It is seldom 
that all the leaves in the same whorl are uniformly 
affected (fig. 58, b and c). The diseased foliage 
or whorls may be irregularly scattered along the 
main stalk. The greatest damage occurs when the 
flowers are spotted, since the plants become un- 
salable whether the leaves are healthy or not. 

Cause. There are many current theories as to the 
cause of the disease. Some growers believe that it is 
due to soil exhaustion. Others believe that it is due 
to the removal of the flower stalks by the growers in 
Bermuda, who desire to sell them, thus giving them 
a double source of profit. It is claimed that this 
practice weakens the bulbs by depriving them of 
their proper nourishment. Still others are of the 
opinion that the bulbs become weakened by being 
harvested prematurely. Finally some growers hold 
that the trouble is due to an insect which feeds on 



Lily Diseases 



279 



the scales of the bulbs. The investigations by 
Woods * have shown that the trouble is brought 
about by a combination of causes. Poor cultural 
conditions such as overwatering, or the use of poor, 
unselected bulbs will generally and indirectly tend 
to cause this disease. The bulbs may be further weak- 
ened by the attacks of a mite {Rhizoglyphus echi- 
nops) and of certain fungi and bacteria. The bulbs 
may also become weakened by allowing the roots 
to dry and then overwater. 

Control. The disease cannot be cured. The best 
that can be done is to select strong, healthy bulbs. 
Crop rotation to prevent the spread of the mite is 
also recommended. 

Rust 

Lilies are subject to several rust diseases. The 
most important is the American rust and is caused 
by a species of Uromyces. This disease according to 
Halsted t was first found on leaves of Lilium can- 
didum at Buffalo, N. Y. 

The Botrytise Disease 
Caused by Botrytis sp. 

Symptoms. The trouble is apparent as small 
rusty spots upon the buds, leaves, and blossoms. 

♦Woods, A. F., U. S. Dept. of Agr. Div. of Veg. Phys. and 
Path. Bui., 14: 7-15, 1897. 

t Halsted, B. D., New Jersey Agr. Expt. Sta., Fourteenth Annual 
Kept.: 392, 1893. 



28o Diseases of Greenhouse Crops 



With the advance of the disease, the spots become 
coated with a fuzzy, brownish coat, made up of 
the fruiting stalks. As the plant becomes decayed, 
numerous sclerotia appear. The disease is spread in 
the hothouse through the watering or in syringing. 
Infection is favored by a high humidity and poor 
light conditions in the house. Little is known of 
the causal organism (fig. 58, d.). 

Control, The disease may be kept in check by 
proper ventilation. 

Call A Lily (Amcea spp.J 

Cultural Considerations. The yellow callas are 
grown in the same way as the white callas except 
that they seem to do better without a rest period. 
White callas require a rich soil, full sunlight and 
an abundance of water during the growing season. 
During the summer, the plants undergo a resting 
period. The pots are laid out in the open in the 
shade and a little water is given occasionally to pre- 
vent the Rhizomes from drying out. 

Diseases of the Calla Lily 

Callas are apparently a hardy plant. It is sub- 
ject to but few diseases. 

Soft Rot 

Caused by Bacillus aroide(Z Town. 

Symptoms, This disease may be found both on 



Lily Diseases 



281 



calla lilies in the greenhouse or in the field. The 
callas usually rot off at or below the surface of the 
ground, the disease frequently spreading downward 
in the direction of the corms and upward into the 
leaves. Occasionally soft rot starts at the edges 
of the leaves or at the flower stalk. The disease 
spreads more rapidly and is also worse in green- 
houses where callas are grown in solid beds. 

In cutting open a diseased corm, one observes a 
line of demarkation between the healthy and dis- 
eased tissue, the latter being brown, soft, and water 
soaked. Affected leaves become slimy without nec- 
essarily losing their green color. If the disease at- 
tacks flower stalks, the flowers turn brown and the 
stalk falls over although its green color is preserved. 
As the disease progresses under ground the plant 
above ground topples over without any sign of dis- 
ease. Under unfavorable conditions, the disease in 
the corm may not progress further than a small spot 
which soon dries. The causal organism, however, 
remains alive in these spots, but dormant until the 
time when conditions of moisture and temperature 
again become favorable. The nature of the soil de- 
termines to a large extent the severity of the rot. A 
soil rich in humus is most favorable for its spread. 

The Organism. Bacillus aroidecz is a short rod 
with rounded ends, single or in chains of two or four. 
Its growth is white on solid media. It produces no 
gas, and liquefies gelatin. Although apparently dis- 
tinct from Bacillus caratovorus Jones, it is neverthe- 
less capable of producing a soft dark colored rot in 



282 Diseases of Greenhouse Crops 



carrot, potato, turnip, radish, cabbage, cauliflower, 
tomato, and in the fruit of eggplant and cucumber. 

Control. The disease may be prevented from get- 
ting a start by discarding diseased or spotted conns. 
Changing the soil every third or fourth year, or 
steam sterilizing it will prevent infection of the 
healthy corms. Starting the plants in pots instead 
of planting them directly in the beds is also recom- 
mended. In this way, all diseased plants will be 
discarded before being put finally in the bed. 

Blight 

Caused by Fhyllosticta ricliardiiZ Hals. 

Symptoms, This disease is characterized by large, 
ashy spots on the leaves. Within these spots may 
be found minute, dark fruiting bodies (pycnidia). 
Very little is known of the causal organism. Blight 
may often be confused with a spotting due to sun- 
scald. In this case, however, the dead tissue is in- 
vaded with the fungus Festalozzia richardicz Hals. 

Leaf Blight 

Caused by Cercospora ridiardiczcola Atk. 

Symptoms, This disease was first found by Pro- 
fessor Atkinson in Alabama in 1 89 1 . The spots are 
black with small white centers, and may be formed 
on all parts of the leaves. 

The Organism, The conidia are hyaline, and from 
4 to 10 septate. The conidiophores are borne in 



Lily Diseases 



283 



bundles and are brownish to reddish in color, finally 
becoming reddish brown with age. 

Control, This disease may be kept in check by 
spraying with a standard fungicide. 

Japan Lily Disease 

Caused by Rhizopus necans Mass. 

Symptoms, This disease is characterized by a soft; 
rot of lily bulbs, especially Lilium speciosum, and 
L. auratum. The malady was studied by Massee * 
who found it on imported bulbs from Japan. The 
causal organism seems to be a wound parasite, that 
gains entrance to the roots through a wound. From 
the roots, it works its way up to the scales and causes 
them to rot. Diseased bulbs generally become cov- 
ered by a white weft of mycelial growth which is 
soon followed by numerous clusters of sporophores 
bearing black globose sporangia. 

The Organism, The mycelium is white, the sporo- 
phores forked or simple. Sporangia globose, black- 
ish to deep brown, columella large. Spores striated, 
pale olive. Zygospores dark, and covered with 
spiny warts. 

Control. WHiere the disease occurs once, the soil 
should not be used again unless it has been sterilized 
with steam or formaldehyde. Injured bulbs should 
not be planted. In shipping bulbs, care should be 
taken that they are not packed damp. 

* Massee, Diseases of Cultivated Plants and Trees: 133, 1910 
(Macmillan Co., New York). 



284 Diseases of Greenhouse Crops 



Blight of the Variegated Plantain Lily 
(Funkia Undulata, var. Variegatd) 

Caused by Colletotrichum omnivorum Hals. 

Symptoms, Th;s blight is severe on the broad 
and the narrow leaved varieties, and especially on 
Funkia undulata var. variegata. The disease ap- 
pears as spots at about the middle of the leaf. The 
tissue in these soon drop out, leaving the veins which 
run lengthwise. Badly diseased foliage have a 
shredded appearance. The same disease also at- 
tacks Aspidistra lurida var variegata, a plant closely 
related to the Funkia. At present, little is known of 
the nature of the causal organism. 

Control, , Halsted recommends spraying with 
Ammoniacal copper carbonate. Attention should be 
paid to securing resistant varieties. 

Lily of the Valley {Convalaria majalis) 

Cultural Considerations, This plant may be 
forced at any time of the year. Sand is the best soil 
in which to grow it. It is advisable to begin with 
a bottom heat of 50 degrees F. and quickly raise it 
to 85 degrees. The plants require an abundance of 
water during the forcing period. 

Diseases of the Lily of the Valley 

Lily of the Valley is considered a hardy plant. 
They are however known to suffer from two diseases. 

♦Halsted, B. D., New Jersey Agr. Expt. Sta., Thirteenth Ann. 
Rcpt: 296, 1892. 



Lily Diseases 



285 



Rot 

Caused by Botrytis p^onicz Oud. 

This disease, which is usually common on peonies 
and on lilacs, also frequently attacks the lily of the 
valley. The causal organism often attacks the pips 
first; then works its way up to the stems. Infected 
pips become soft, then become covered with a gray- 
ish mold, and are later peppered with greenish-black, 
flat sclerotia. 

Control, The disease is often introduced with in- 
fected pips which have been previously injured, or 
kept under poor storage conditions, especially under 
too high temperatures and moistures. Hence only 
healthy pips should be used. If the soil becomes in- 
fected with the causal organism, it should be steam 
sterilized, or treated with formaldehyde (see pp. 32- 
43) the former method being preferred. 

Leaf Spot 

Caused by Dendrophoma convallaritz Can. 

This leaf spot often destroys entire beds of plants. 
Little is known of the causal organism or of methods 
of control. 

Septoria Leaf Spot 

Caused by Septoria majalis Aderh. 

This disease is characterized by a general spot- 
ting which is unevenly scattered over the leaves. The 
spots, however, are found mostly on old and faded 



286 Diseases of Greenhouse Crops 



leaves, hence the trouble is of no economic impor- 
tance. 

Mignonette {Reseda odoratd) 

Cultural Considerations, The soil required for 
mignonette is about the same as for carnations. 
Raised benches are preferred rather than pots. An 
inch of well rotted stable manure is placed at the 
bottom, and four inches of the compost on top. 
Young seedlings require an abundance of ventilation. 
During bright weather temporary shading is neces- 
sary. Mignonette is very sensitive to overwatering. 
The watering should be done in the morning. If 
water remains on the foliage over night, the plants 
will become badly spotted. The temperature of the 
house in cloudy days should not run above 55 degrees 
F. and in bright days not higher than 65 degrees. 

Diseases of the Mignonette 

Mignonette is subject to but few diseases. The 
most important of these may be mentioned as fol- 
lows : 

White Rust 

Caused by Cystopus Candida (Pers.) Roussel. 

This disease is commonly met with out of doors 
on practically all cultivated cruciferous plants. In 
Europe, white rust seems to attack the mignonette, 
but there are no records of similar cases in the United 
States. 



Mignonette Diseases 287 



Leaf Spot 

Caused by Cercospora resedcz Fl. 

Symptoms, The trouble becomes apparent as 
minute pale spots with yellowish to brownish bor- 
ders. In spreading over the entire leaf, it takes on 
a reddish discoloration. Usually, the lower leaves 
are most affected. Little is now known of the causal 
organism. 

Root Rot 

Caused by Rhizoctonia sp. 

Root rot of mignonette may be expected wherever 
the soil in the benches is infected with Rhizoctonia. 
The young plants usually damp off. Older ones rot 
at the base of the stem and at the roots. In either 
case, affected plants are dwarfed, and the leaves have 
a sickly yellow color. For a description of the or- 
ganism and for methods of control, see p. 20. 

Narcissus {Narcissus bulbocodium) 

Cultural Considerations, Narcissus is easily 
forced. After potting, a thorough watering should 
be given, as the bulbs fail to set roots in a dry soil. 
The pots should be placed in a cool cellar to en- 
courage root formation and to retard top growth. 
After bringing the pots into the greenhouse, they 
should at first be placed under the benches or under 
subdued light, and in a low temperature of about 
50 degrees F. Later the plants are gradually ex- 



288 Diseases of Greenhouse Crops 



posed to more light. The more slowly they are 
forced the better the quality of the flowers. Dur- 
ing the blossoming period great care should be given 
to the watering. At no time should the root system 
be permitted to become dry. On bright days the 
tops of the plants should be syringed until the flow- 
ers begin to show color. 

Diseases of the Narcissus 

Narcissus under normal care is very hardy and 
subject to very few diseases. 

Rust 

Caused by Fuccinia schroeteri Pass. 
This rust often attacks Narcissus poeticus. It is 
of no economic importance in the United States. 

Bulb Rot 

Caused by Fusarium hulhigenum Mass. 

Symptoms, This trouble, which was studied by 
Massee,* is said to be prevalent in England. Its 
presence in the United States has not been reported. 
The trouble first appears on the leaves as small 
yellowish spots. These, however, enlarge and work 
downward into the bulb scales, the latter of which 
soon rot. The disease is spread by partly diseased 

♦Massee, G., Roy. Bot. Gard. Bui. Misc. Inf.: 307-309, 1913. 



Narcissus Diseases 289 



bulbs and through infected soil. Little is now 
known of the causal organism. 

Control. Care should be taken to prevent the in- 
troduction of this disease into this country. All 
bulbs which show the least discoloration should not 
be used for planting. 



CHAPTER 24 



ORCHIDS {Orchidacea) 

Of the numerous orchids, the following arc the 
important commercial genera with their cultural 
requirements : 

Culture of Calanthe 

These are easily grown in pots or in beds, about 
one-third space being devoted to drainage by m^eans 
of a layer of clean sphagnum. The pseudobulbs 
are then planted in a compost which is made up of 
one-third chopped sod with the fine soil removed, 
one-third chopped live sphagnum and leaf mold to 
which charcoal is added as a sweetener. Calanthes 
require a winter night temperature of about 50 to' 
55 degrees and a day temperature of 65 to 70 de- 
grees F. The plants require an abundance of water 
during the growing period, but less when the leaves 
start to drop and blossoming begins. At this stage, 
only enough water is needed to keep the blossoms 
from wilting. When the blossoming season is over 
the plants are given a six weeks' rest. The pots 
with the pseudobulbs are laid on the side in a dry 
warm place and the soil kept dry. 

290 



Orchid Diseases 291 



Culture of Cattleya 

These plants require perfect drainage conditions. 
They thrive best in osmunda fiber pots. On a com- 
mercial scale, it is not desirable to cover the plants 
with moss as this usually harbors slugs which are 
fond of the blossoms. Cattleyas require frequent 
syringing with the hose. The temperature required 
is the same as that for Calanthe. After flowering 
the pseudobulbs need a rest. In this case they re- 
quire enough water to prevent them from drying. 
Cattleyae thrive best when grown near the glass. 

Culture of Ccelogyne 

The cultural requirements are the same as for 
Cattleyse, the pot culture, however, being preferred. 
The plants are heavy feeders, hence weak manure 
water may be applied once every week during the 
growing season. After flowering the plants are re- 
potted and kept in a cool house until about Sep- 
tember. 

Culture of Cypripedia 

These plants require no rest period, hence may 
be grown the year round. They require a winter 
night temperature of 60 to 65 degrees F. and a 
day temperature of about 70 degrees F. As spring 
approaches a higher temperature may be given, and 
the glass lightly shaded. However, in the winter 
the plants require the full sunlight. 



292 Diseases of Greenhouse Crops 



Culture of Dendrobium 

These plants seem to thrive best in small pots or 
baskets. They also require an abundance of water 
during the growing season, and a night temperature 
of about 65 degrees F. When flowers appear the 
plants become destitute of leaves, at which time 
only enough water is applied to prevent the pseudo- 
bulbs from drying. 

Culture of Li5:LiA 

These plants require a sunny location and an 
abundance of overhead water during active growth. 

Culture of Lycaste 

These plants need to be kept as cool as possible 
in the summer; otherwise, the culture is the same 
as for Cattleya. 

Culture of Odontoglossum 

These plants require an abundance of ventilation, 
and a cool moist temperature during the summer. 
They are grown in pots or baskets filled with soil 
made of equal parts peat, live sphagnum moss, and 
osmunda fiber. 

Culture of Oncidium 

These plants require a bright, warm house and 
are suspended from the rafters in small baskets. 



Orchid Diseases 



293 



Culture of Phal.5:nopsis 

These plants require plenty of ventilation, but too 
much of it should be avoided. Frequent syringing is 
necessary and the temperature requirements from 70 
to 75 degrees F. at night and about 90 to 95 degrees 
during the daytime. 

Culture of Vanda 

These plants require shade after February. They 
prefer a night temperature of 65 degrees F. and seem 
to thrive best in baskets near the glass. 

Spot Disease of Orchids 
Cause, mechanical injury. 

Symptoms, This disease is manifested as minute 
pale spots on the upper side of the leaf. The spots 
vary considerably in size, arrangement, and num- 
bers, and may occur on any parts of the foliage irre- 
spective of age. The trouble may be easily over- 
looked, due to the light color and the superficial na- 
ture of the spots. With age, however, the spots 
may go through the entire tissue of the leaf. The 
cause of the trouble, as explained by Massee,* is of 
non-parasitic origin. It is brought about by the 
presence of minute drops of water on the surface of 
the leaves during very low temperatures while the 
roots are too copiously supplied with water. The 

♦Massee, G., Anoals of Bot. 9:423-429, 1895. 



294 Diseases of Greenhouse Crops 



water drops produce a chill which causes the content 
of the underlying cells to plasmolyze. This is fol- 
lowed by the precipitation of tannin and the disin- 
tegration of the cells. The method of control would 
consist in the careful watering of the plants during 
cool weather. 

Orchid Deterioration 
Cause, cultural. 

Florists are aware of the fact that imported or- 
chids often run out and deteriorate after a year or 
two of culture under glass. Attention has been 
called to a similar trouble by Truffant and Hebert.* 
They maintain that deterioration is due to an in- 
crease in the percentage of mineral matter and a de- 
crease in the percentage of nitrogen in the deterio- 
rated plants. The trouble, it is believed, is due 
largely to improper nutrition under cultivation. 

Leaf Spot of Orchids 
Cause unknown. 

This disease is often found on hybrid Calanthes. 
It is manifested as large and small dead patches 
on all the parts of the plant. The leaves especially 
become unsightly, and as a result the blossoms are 
small and stunted. This disease was first described 
by Bidgood t on greenhouse hybrid Calanthes. The 

♦Truffant, G., and Herbert, A., Jour. Soc. Nat. Hort. France, 19: 
85-98, 1897. 

t Bidgood, J., Jour. Roy. Hort. Soc. 29: 124-137, 1904. 



Fig. 59. Orchid Diseases. 

a. Volutella blight of Bletia (after Halsted), h. rust, Hemileia oncidi (after 
Griffon and Maublanc), c. Sobralia anthracnose (after Halsted), d. bacterial leaf 
spot, partly diseased leaf with cells invaded by the organism (after Hori, S.). 



Orchid Diseases 



295 



cause of the disease and methods of control are as 
yet unknown. 

Bacterial Leaf Spot of Orchids 

Caused by Bacillus cypripedii Hori. 

Symptoms. According to Hori,* this disease is 
prevalent in Japan and is greatly feared there. The 
disease attacks the most valuable orchids and ruins 
them in a very short time. 

The disease is manifested as light amber-colored 
spots on the leaf blades. The spots quickly enlarge, 
and in a few days the entire leaf becomes invaded 
and discolored. A few days later the diseased foli- 
age turns brownish and later a deep chestnut 
brown ; the upper surface becomes wrinkled, . with 
loss of luster. The lower surface of the leaves, just 
underneath the spots, rapidly take on a faintly pale 
color, and only gradually assumes the same color 
as that of the upper part. If infection takes place 
on the lower portion of the leaf, the upper half 
soon becomes yellowish and dies off as a result of 
lack of food (fig. 59, d.). The rot from the leaves 
works down to the stem, involving the entire plant. 

The disease (also known as brown rot, brown 
spot) attacks orchids with fleshy, succulent leaves, 
such as Phalsenopsis amabilis. Ph. schileriana Cyp- 
ripedium haynaldium, C. philippinense, C. Iseviga- 
tum, C. godefroyae. The more susceptible varieties 
seem to be Phalsenopsis schilleriana and Cypripedmm 

*Hon, S., Centralb. fur Bakt., 31:85-92, 191 1. 



296 Diseases of Greenhouse Crops 



phillipinense. Infection takes place by means of 
a wound. 

The Organism. Bacillus cypripedii is a medium 
sized slender rod-shaped organism, rounded at both 
ends, occurring in chains of 2-3, and motile by- 
means of flagella. On agar it forms a smooth, light 
grayish white colony with a pearly luster, and a 
dirty cream-colored growth on potato plugs. It pro- 
duces a film on bouillon, coagulates milk, and rap- 
idly dissolves gelatin. It is not known whether the 
causal organism is the same or closely related to the 
one described by Peglion * under the name of Bac- 
terium oncidii Peg. as causing a disease on orchids. 
Very little is known of the methods of control. 
Since infection takes place through a wound, care 
should be taken to prevent careless washing with a 
rough sponge. Diseased material should be de- 
stroyed by fire. 

Rust of Orchids 

Caused by Hemileia oncidii Griff and Maubl. 

Symptoms. The disease is characterized by mi- 
nute yellowish spots, the surfaces of which become 
covered with an orange-colored powder which is 
made up of the spores of the causal organism. The 
spots enlarge, the center turns brownish, while 
the advancing margin remains an orange rust color. 
The disease was first described by Griffon and Mau- 

* Peglion, v., Centralbl. fiir Bakt. 5:33, 1899. 



Orchid Diseases 297 



blanc,* who found it on orchids in greenhouses in 
France. It is not known whether this rust is of any 
importance in the United States. The only danger 
consists in its being imported from abroad with im- 
ported plants. The causal organism produces only 
teleutospores. It feeds on its host by means of 
haustoria sent into the interior of the cells (fig. 59, 
d, 1-9.). 

Rust of Orchids 

Caused by Uredo behnickiana Henn. 

Symptoms, This rust does not produce any strik- 
ing symptoms. Hence it may readily be overlooked. 
Affected leaves are covered with minute, reddish- 
colored sori. When mature, the epidermal covering 
of these sori breaks away and liberates a reddish 
powder which is made up of thousands of the spores 
of the fungus. This rust is found on living leaves 
of Oncidium dasystelis and was described by Hen- 
nings t as a serious disease of orchids imported to 
Germany from Brazil. It is not known whether this 
disease is present in this country. Its introduction 
should therefore be guarded against. Uredo be- 
hnickiana differs from U, onicidii Henn, in that the 
latter causes rounded thickened red-brown spots on 
Oncidium lavecanum. 

♦Griffon, M. M., and Maublanc, Bui. Soc. Mycol. de France 25; 
135-139, 1909. 
t Hennings, P., Hedwigia 44:169, 1904. 



298 Diseases of Greenhouse Crops 



Petal Blight 

Caused by ScJeroti/iia fuckeliana (De By.) Fckl. 

Greenhouse growers are often troubled with a 
petal blotch of orchids. This disfigures the blos- 
soms, and consequently ruins their market value. 
The disease appears as small spots over the entire sur- 
face area of the petals. Frequently the spots are bor- 
dered by a delicate ring of pink. Perhaps another 
stage of this disease is marked by the large spots 
which cause the petals to become disorganized. Af- 
fected petals either drop off or stick to the now 
worthless blossom. On examination of the spotted 
petals, there will be noticed a gray mold growing on 
the surface of the affected tissue. This is but the 
fruiting stalks of the causal organism. This gray 
mold will also be found on faded blossoms, and if 
allowed to remain in the greenhouse will saturate 
the place with the spores of the fungus. 

Control. All affected blossoms should be cut off 
and destroyed. This simple precaution will remove 
the host upon which the fungus is able to thrive as 
a saprophyte. 

Rot 

Caused by Nectria huJhicoJa Henn. 

This trouble is manifested as a rot on the pseudo 
bulbs of Macillaria rufescentis. It was originally 
found by Hennings"^ on orchids brought in from 
Venezuela or Trinidad. 

* Hennings, P., Xotizbl. K. Bot. Gasten u. Mus. Berlin. 



Orchid Diseases 299 



There are other Nectria recorded on orchids: 
Nectria vand^ Wahrl on root of Vanda suavis, 
Nectria goroshankianna Wahrl., Nectria {Dialo' 
nectria) binotiana Sacc, and Nectria (D.) phyllo- 
gena Sacc. on leaves of epiphyte orchids in Brazil. 

Anthracnose of Orchids 

Caused by Fhysalospora cattley^ Maub. and Las. 

Symptoms, This trouble is manifested as yellow- 
ish light spots the tissue of which becomes soft. 
When the epidermis is torn away from one of the 
spots a clear liquid will ooze out. At this stage 
of the malady infected leaves lose their normal 
color, collapse, and drop off. Ordinarily there is 
no fruit of any fungus formed on the spots, but 
under moist conditions the acervuli of the causal 
fungus appear. The disease, although attacking the 
foliage, does its greatest damage to the stems. In- 
fection can take place only through a wound made 
in the epidermis. 

The Organism, It is only the summer stage of 
the fungus, Gloeosporium macro pus Sacc, which 
causes the disease on orchids. The same stage also 
produces a similar disease on foliage of Haya car- 
nosa. Citrus aurantium and Aloes. Its occurrence on 
orchids was called attention to by Mangin,* who 
found it to be a serious disease of greenhouse orchids 

♦Mangin, M. L., Jour. Soc. Nat. d'Hort. de France 19: 449-452, 
1897. 



300 Diseases of Greenhouse Crops 



in France. It is doubtful if it is yet to be feared 
in the United States. 

ControL Care and vigilance should be exercised 
to prevent the introduction of the disease to the 
United States. All infected material should be de- 
stroyed by fire and the plants should be sprayed with 
a standard fungicide. 

American Anthracnose 

Caused by Glomerella cincta (B. and C.) S. 
and S. 

The American anthracnose is very prevalent on 
hothouse orchids. The variety most susceptible to 
the disease is Sobralia macramtha. The trouble is 
first noticed by a discoloration on the stems which 
soon become brown almost to black while the tender 
interior tissue becomes soft and decayed. Later 
the spore pustules appear in great abundance on 
the dead parts. On the leaves the disease works 
in a way similar to that found on the stems. The 
trouble, however, nearly always starts from the tip 
and works downwards (fig. 59, c). There is usu- 
ally a distinct line of demarkation between the 
healthy and the diseased tissue. 

The Organism, The conidial or summer stage 
of the fungus was described by Halsted.* The 
conidia are elliptic and guttulate. Setse may often 
be present, but they are generally obscured by the 

* Halsted, B. D., New Jersey Agr. Expt. Sta., Fourteenth Ann. 
Kept.: 414-415, 1893. 



Orchid Diseases 301 



great masses of spores formed in the acervuli. The 
ascus or winter stage was discovered by Stoneman.* 
The perithecia are flask-shaped, the asci are clavate. 
The ascospores vary from elliptic to curved in shape. 

Control. Before attempting anything else, the 
source of infection should be removed. All infected 
plants should be destroyed by fire. Spraying with 
Bordeaux mixture 4-4-50 will help to protect the 
plants from becoming infected. 

Bletia Anthracnose 

Caused by Colletotrichum bletice Hals. 

The beautiful Bletia orchid is often subject to 
the attacks of an anthracnose, the cause of which is 
due to a closely associated organism of the Sobralia 
anthracnose. On the Bletia, the trouble is mani- 
fested as a spotting that disfigures the leaves and 
reduces their usefulness. The spots are almost black 
and very soft. As this disease progresses, the soft 
tissue rots and breaks away the fibrous portions. 
Usually the trouble begins at the tender tips, and 
causes affected foliage to have a ragged appearance. 

The Organism, In structure the organism resem- 
bles other Colletotrichums. The acervuli are light 
brown in color and possess numerous dark setse. 

Control, The trouble may be kept in check by 
spraying with Bordeaux mixture. It is also essen- 
tial to destroy by fire all dead and diseased material 

* Stoneman, B., Bot. Gaz. 26: 69-120, 1898. 



302 Diseases of Greenhouse Crops 



and to prevent them from finding a place in the 
manure or compost pile. 

European Anthracnose 

Caused by Glceosporium affine Sacc. 

This disease has been reported by Sorauer* as 
very serious on cultivated orchids. The trouble is 
prevalent in overheated hothouses and on plants 
which have been excessively fertilized. 

Symptoms. On the leaves, anthracnose causes a 
discoloration and a drying which starts at the tip, 
or at the periphery or border. Usually the young- 
est foliage is attacked first. In severe cases, the 
older leaves and even the bulbs become diseased, 
wither, and dry up. The disease is carried about 
with infected bulbs. The same trouble also attacks 
other orchids such as Cattleya Mendelii and Cypri- 
pedium Isevegatum. 

The Organism, In structure, Glceosporium affine 
differs very little from other Gleosporiums. The 
fungus attacks the epidermis, then works into the 
mesophyllic layer of cells, where the chloroplasts are 
destroyed. This explains the disappearance of the 
green coloring matter in the affected parts. The 
spore pustules are formed under the epidermis, the 
latter bursting as the spores accumulate. The spores 
are formed on what appears to be a pseudostroma. 
The spores are one-celled, hyaline, cylindrical, and 

*Sorauer, V. P., Zeitsch. Pflanzenkr. 21:387-395, 1911. 



Orchid Diseases 303 



often slightly curved. The spores germinate 
quickly, usually after forty-eight hours. Glceospo- 
rium affine is troublesome on orchids in Europe, but 
has not yet proved very serious in the United States. 

Other Orchid Glceosporiums 

Glceosporium oncidii Oud.= G. maxillaricz All. 
This organism is confined to leaves of Maxillaria 
infestans. 

Glceosporium epidendri} Henn. This organism 
attacks stems of Epidendrum sp. 

Glceosporium stanhopea AUesch. is found on 
leaves of Stanhopese. 

Glceosporium Idlicz Henn. is found on leaves of 
Laelia sp. 

Glceosporium pallidum Karst. and Har. occurs on 
leaves of Liparis longipes. 

Colletotrichum orchidearum K. and H. appears on 
leaves of Bolbophyllum labbi, B. longiflorum. It 
is also found on foliage of Cymbidium sp., Physio- 
phon loddigesii ; Ezia stelleta, Coelogyne mayeriana, 
Pleurothallis tribuloides, Sarcanthus pugioniformis, 
on pseudobulbs of Eulophia saundersiana and on 
Oncidium pulvinatum. 

Colletotrichum dichecz Henn. grows on foliage 
of Dichsea vaginata. 

Colletotrichum roseolum Henn. develops on the 
pseudobulbs of Stanhopea oculata. 



304 Diseases of Greenhouse Crops 



Leaf Spot of Orchids 

Caused by Cercospora angreci Roum. 

Symptoms. This disease is usually manifested as 
spots which are more prominent on the underside 
of the leaves. As the affected foliage turns pale 
and loses its green color, the spots become covered 
with a chocolate-colored mold. The latter growth 
consists of the fruiting stalks and conidia of the 
fungus. Cercospora angreci is found on foliage of 
Odontoglossum alexandrse. Little is now known of 
the causal organism and of methods of control. 

Bletia Leaf Spot 

Caused by Volutella concentrica Hals. 

Associated with the anthracnose ( Colletotrichum 
bleti(z) is often found a leaf spot which may be 
mistaken for it. The characteristic of this disease 
is the formation of large dark spots (fig. 59, a.). 
Each spot is made up of numerous bluish-colored 
concentric rings. The fruitings of the fungus ap- 
pear as lemon-colored balls. It is not definitely 
known whether the Volutella fungus is an active 
or a weak parasite merely following some injury, 
or the attacks of a bacterial organism. In fact little 
study was given to this trouble and the only record 
that exists is a note by Halsted."^ 

•Halsted, B. D., New Jersey Agr. Expt. Sta., Fourteenth Ann. 
Kept.: 417, 1893. 



Orchid Diseases 305 



Fungi Found on Orchid Leaves 

The following are fungi found by Hennings* on 
dead orchid leaves : 

Physalospora orcliidearum Henn. This fungus is 
found on dead stems of orchids of Tainise stellatse 
and Laelia schilleriana. It is probable that the fun- 
gus Fhysalospora herbarum (Pers.) Rab. found on 
dead stems of Phajuswallichii is the same as P. 
orcliidearum. 

Pleospora orchidearum Henn. This fungus is 
found on dried-up stems of Phajuswallichii. 

Nectria {Dialonectrid) bolbophyli Henn. This 
fungus is found on dead pseudo-bulbs of orchids of 
Bolbophyllum lobbii. 

Nectria behnickiana Henn. This was found on 
orchids imported from Brazil. 

Macrophama oncidii Henn. This fungus was 
found on dead leaves of Oncidium pulvinatum. 

Macrophoma cattleyicola Henn. This fungus was 
found on pseudo-bulbs of Cattleya labiata. 

Diplodia sobralice (Henn.) Taub.t Found on 
dead leaves of Sobralia scssilis. 

Other Fungi Found on Orchids 

Stibella bulbicola Henn. is found on pseudo-bulbs 
of Gomeza plantifolia, Stanhopea spec, Sarcanthus 
pugioniformis, Epidendrum spec, and on Oncidium 
pulvinatum. 

* Hennings, P., Hedwigia 44: 169-174, 1904 

t See Taubenhaus, J. J., Amer. Jour, of Bot. 3: 324-331, 1915, 



3o6 Diseases of Greenhouse Crops 



Graphium hulhicola Henn. occurs on pseudo- 
bulbs of Oncidium pulvinatum. 

Tubercularia cattleyicola Henn. grows on stems 
of Cattleya guttata. 

Sclerotium orchidearum Henn. develops on stems 
of Vanda tricolor, and Dichsea vaginata. 

Diplodia hulhicola Henn. Found on dead 
pseudo-bulbs of Gomeza plani folia. \ 

Zythia nepenthis Henn. Found on dead leaves 
of Nepenthes bicolorarta. Of the other fungi which 
are often found on dead foliage of Nepenthes may 
be mentioned Fhyllosticta nepenthe ace arum Tassi, 
and Fhoma nepenthis Cook and Mass. Humaria 
thozetti Beilkj., Excipularia epdendri Hennc 
Found on dead foliage of Epidendron. 

OxALis {Oxalis hoiviei) 

Cultural Considerations. Oxalis is forced mainly 
as a window plant grown in baskets or pots. It 
requires a rich soil and an abundance of water. 
The flowers open only when exposed to full light. 

Fungi Recorded on Oxalis 

The Oxalis is a very hardy plant. The following 
are the fungi recorded on the host: JEcidium oxali- 
dis Thuem., Darluca filum (Biv.) Cast., Fuccinia 
oxalidis Diet, and Ell., Urocystis oxalidis Pazs. 

Palm {Fhcanix spp.) 

Cultural Considerations. Palms are very sensi- 
tive to wet and poorly drained pots or benches. 



Palm Diseases 



307 



The soil best suited to palm culture is that which 
is made up of two-thirds rotted sod and one-third 
well rotted cow manure. Palms do poorly when 
treated with commercial fertilizers, and when its 
root system is disturbed, hence they should be re- 
potted only when absolutely necessary. Palms love 
partial shading (fig. 60) and a moist atmosphere. 
The temperature should be allowed to go below 60 
degrees F. at night. The foliage should be kept 
free from dust. 

Diseases of Palms 

Forced palms are subject to less disease than 
those grown out of doors. Nevertheless, some of 
these indoor diseases often become very troublesome 
and serious. 

Smut 

Caused by Graphiola pJicenicis Port. 

Symptoms. Smut is a common disease on both 
greenhouse and outdoor palms of all sorts. The 
affected areas on the leaf become mottled with yel- 
low, and upon the surface pustules appear (fig. 
61, a.). These are cup-shaped conceptacles pro- 
duced by the causal fungus, and in which the spores 
are borne. The spore pustules consist of a firm, 
dark colored exterior wall, enclosing a more deli- 
cate inner covering which contains a mass of thread- 
like filaments on which the spores are produced 
(fig. 61, b.). The spore pustules become very nu- 
merous and the affected foliage slowly shrivels. 



3o8 Diseases of Greenhouse Crops 



Control, All diseased material should be de- 
stroyed by fire. Some florists recommend spraying 
or sponging the leaves with potassium permangan- 
ate. 

Anthracnose 

Caused by Colletotrichum kenticz Hals. 

This disease has been first studied by Halsted* 
as it was found by him to attack the various orna- 
mental Kentias. 

Symptoms, The disease appears as watery spots, 
which soon become dry (fig. 61, h) and within 
which are formed the salmon-colored acervuli which 
contain numerous sets. In time the dead tissue 
falls out, leaving holes in which remain the hard, 
woody vessels which run across. This disease also 
attacks young seedlings and cripples them beyond 
any commercial value. The following Kentias are 
subject to the attacks of the anthracnose: Kentia 
belmoreana, K. canterburyana, and K. fosteriana. 

Control, It is difficult to keep this disease in 
check unless the infected material is removed and 
destroyed by fire. Spraying the plants weekly with 
a standard fungicide will keep the anthracnose in 
check. 

ExospoRiuM Leaf Spot 

Caused by Exosporium palmivorum Sacc. 
Symptoms, The disease is characterized by mi- 

* Halsted, B. D., New Jersey Agr. Expt. St., Fourteenth Ann. 
RepL: 407-409, 1893. 



Fig. 6i. Palm Diseases. 

a. Palm smut, b. Palm smut fungus (after Stone and Smith), c. Exospo- 
rium leaf spot, d. cluster of spores of Exosporium pahnivorum, e. individual 
spores of E. palmivorum, f. conidiophores of E. palmivorum {d-e after Tre- 
lease) g. Sphaerodothis leaf spot (after Smith, R. E.), h. anthracnose (after 
Halsted). 



Palm Diseases 309 



nute brown spots. These are often so numerous as 
to involve the entire leaf, causing it to dry up and 
die (fig. 61, c). This trouble is very common 
on greenhouse palms, especially on those which 
are kept in too long under shade. It is common 
on Phoenix canariensis, on P. tenius and on P. re- 
clinata. The disease undoubtedly must have been 
introduced from Europe with imported stock. Tre- 
lease"^ observed it in America in 1897. 

The Organism. The sporodochia are superficial 
black, and dense (fig. 61, d), visible to the naked 
eye as a black mold. The spores are borne singly, 
are olive brown in color, and are many times sep- 
tate (fig. 61, e and f..). 

Control, The disease seldom occurs in well 
lighted and well ventilated greenhouses. Where 
the disease makes its appearance, more attention 
should be given to the ventilation, and the shad- 
ing should be gradually diminished. All infected 
material should be cut off and destroyed by fire; 
the plants should be sprayed with a standard 
fungicide. 

Leaf Blight 

Caused by Festalozzia palmarum Cke. 

Symptoms. This disease appears as transparent, 
dirty white spots at the tip of the leaflets or at 
the axils. The spots spread quickly and it is not 
uncommon to find numerous leaves killed, and the 
affected plant thereby badly disfigured. As the 

♦Trelease, W., Rept Mo. Bot. Gard. 9: 159, 1898. 



310 Diseases of Greenhouse Crops 



affected tissue dries, the spore masses are formed 
on the upper part of the leaflets and appear as a 
black exudate. 

Control, Infected material should be cut out and 
destroyed by fire. Infected plants should not be 
syringed, for hi this way the spores of the causal 
organism are spread wholesale. Spraying with a 
standard fungicide is also recommended. 

Leaf Spot 

Caused by Sph^rodithis neo washing tonia. 
The disease is mentioned by Smith* as occurring 
in California. The leaves become covered with 
small elongated, black, slightly elevated spots 
(fig. 61, g.). Affected leaves should be removed 
and burned, and the plants sprayed with a standard 
fungicide. 

Pansy {Viola tricolor). 

Cultural Considerations, Pansies are grown 
mostly out of doors. Occasionally, however, flor- 
ists raise them indoors as pot plants for purposes 
of window decoration. Its cultural requirements 
are about the same as for the violet (see p. 351). 

Diseases of the Pansy 

Pansies, like violets, are subject to about the same 
diseases. 

* Smith, R. E., and Smith, E. H., California Agr. Expt. Sta., 
Bui. 21S: 1148, 191Z. 




Fig. 62. Pansy Diseases. 

a to f. Colletrotrichum violce-tricoloris R. E. Smith, a. affected leaf- 
let, h. several confluent acervuli with mycelium, setae, and conidia. c, 
single acervulus, more enlarged, d. basidia and production of conidia, 
e. conidia, f. affected blossoms, g to i. Fusarium violcc. Wolf, g. forma- 
tion of microconidia, h. germination of macroconidia, i. macroconidia 
(o-/ after Smithy R. E.; g to i after Wolf, F. A.). 



Pansy Diseases 311 



Anthracnose 

Caused by CoUetotrichum viola-tricoloris R. E. 
Sm. 

Symptoms, The disease attacks the petals, and 
affected flowers become deformed, and fail to pro- 
duce seed. This is a serious consideration especially 
from the seedman's point of view. The spots on 
the leaves (fig. 62, a) are small with prominent 
margins. 

The Organism. The acervuli are numerous, the 
stroma poorly developed, and the setae mostly sin- 
gle or in pairs, short, two septate and deep brown 
in color. The conidiophores are short, the conidia 
oblong or slightly curved, with blunt ends (fig. 62, 

b-f.). 

Control, The disease is usually introduced with 
the seed. All shriveled seed should therefore be 
discarded, and the healthy ones soaked for five min- 
utes in a solution made of one ounce of formalde- 
hyde in twenty gallons of water. Diseased plants 
should be destroyed by fire. Pansy beds where 
anthracnose is present should be kept on the dry 
side of the house. The plants should not be 
sprinkled with water, as in this way the spores of 
the causal fungus may be spread about. Healthy 
plants may be protected by spraying with a standard 
fungicide. 

Leaf Spot 

Caused by Cercospora viola Sacc. 

Symptoms. This disease appears as small dead 



312 Diseases of Greenhouse Crops 



spots surrounded by a definite black border. The 
spots soon enlarge and when very numerous cause 
the premature death of the foliage. The trouble 
is also met with on the blossoms; the petals in this 
case become spotted and blotched. Affected young 
blossoms become distorted or fail to open altogether. 

The Organism, The conidiophores of the fun- 
gus are short, simple and grayish. The conidia are 
long, slender, rod shaped, hyaline, and many 
septate. 

Control, It is claimed by Stone and Smith* that 
good results were obtained by spraying with Bor- 
deaux. The latter, however, is objectionable be- 
cause of its staining the blossoms. Ammoniacal 
copper carbonate may therefore be used instead. 
Spraying may be done at intervals of every two 
weeks. All dead and infected material should be 
destroyed by fire. 

Root Rot 

Caused by Fusarium violcz Wolf. 

This disease causes a rot of the roots and stems. 
The causal organism (fig. 62, g to i) is usually 
brought in the house with infected compost. As a 
control measure soil sterilization is recommended 
(see pp. 32-43). 

♦Stone, G. E., and Smith, R. E., Mass. (Hatch) Agr. Expt. 
Sta. Ann. Rept. ii: 152, 1898. 



Pansy Diseases 313 



Crown Rot 

Caused by Rhizoctonia solani Kuhn. 

Crown rot first appears in the form of minute 
lesions at the crown of the plant. These enlarge 
and penetrate the tissue deeply until the plant is 
practically girdled. Rotting usually sets in, where- 
upon the prostrate branches, the leaves, and peti- 
oles also rot. For a description of the causal or- 
ganism and for methods of control, see p. 20. 

Pandanus or Screw Pine (Pandanus veitchiz) 

Cutural Considerations. Screw pines are forced 
extensively and are used as ornamental house 
plants. They require a temperature of 65 to 70 
degrees F. and must be exposed to full light, espe- 
cially in the winter. The plant flourishes best in a 
soil composed of two parts of heavy loam and one 
part of thoroughly rotted cow manure. The soil re- 
quired is a heavy loam to which is well worked in 
one-third of thoroughly rotted cow manure. 

Diseases of the Pandanus, Pandanus is consid- 
ered a very healthy plant. There are, however, 
two fungi that proved injurious; these are Nectria 
pandani Tul. and Melanconium pandani Lev., 
which are known to be parasites. 

PoiNSETTiA {Euphorbia pulcUerima) 

Cultural Considerations. Poinsettias are exten- 
sively grown for the Christmas trade. The plants 



314 Diseases of Greenhouse Crops 



prefer a soil consisting of fibrous loam, one-fourth 
of which is well rotted cow manure. Poinsettias 
require frequent repotting to prevent them from be- 
coming potbound. The night temperature should 
never go down below 55 degrees F. As the plants 
advance in age, the temperature is raised to 65 or 
70 degrees. A few days before Christmas the stock 
should be ready and the temperature lowered to 
50 degrees F. Great care should be exercised to 
prevent the potted plants from becoming either 
overwatered or too dry. Poinsettias that are to 
be used for cut flowers should have the stem end 
dipped in hot water for a few moments and then 
placed in cold water. This procedure will cauter- 
ize the wounds and thus will add to the keeping 
qualities of the blossoms. 

Diseases of Poinsettias 

Poinsettias seem to be remarkably free from dis- 
eases. This is especially true as the plants outgrow 
the cutting stage. 

Collar PiOT 

Caused by Rhizoctonia solani Kuhn. 

Sympto7ns, The trouble is confined mostly to 
cuttings that have been planted in an infected soil. 
The lesions unite and in nearly every case form a 
collar around the stem on the surface of the soil. 
The collar formed is narrow, depressed, and dark 
in color. For a description of the causal organism 
and methods of control, see p. 20. 



CHAPTER 25 

PRIMROSE {Primula sinensis) 

Cultural Considerations, Young seedlings are 
greatly injured if the compost contains unrotted 
manure. When the plants begin to grow rapidly 
a little bone meal may be worked into the soil. 
During the blossoming period a little weak liquid 
manure may be given, but only when the leaves are 
pale. In transplanting, the crown of the plant 
should not be planted too deeply in the soil lest it 
rot. Neither should it be planted too high lest it 
fall over. After transplanting primroses need 
shade. Later, however, they should be given the 
benefit of full light and ventilation. The soil 
should never be allowed to become dry. 

Diseases of the Primrose 
Primroses are subject to several serious diseases. 

Spot Decay 

Caused by Sclerotinia fuckeliana (De By.) Fckl. 

Symptoms, The conidial stage, Botrytis vulgaris^ 
of this fungus causes a spot decay on the foliage 
(fig. 63, a.). The fungus often thrives on old 

315 



3i6 Diseases of Greenhouse Crops 



and faded blossoms. These, therefore, act as a 
source of infection. It is needless to add that clean- 
liness will form a part of the control method. 
Spraying with any of the standard fungicides is also 
recommended. 

Anthracnose 

Caused by Colletotrichum primulcz Hals. 

Symptoms, Affected leaves become brown and 
spotted. The spots are more visible on the lower 
part of the foliage (fig. 63, c). The acervuli 
with its black setse of the causal organism are 
especially conspicuous when looked at with a mag- 
nifying lens. At present little is known of the 
organism. The disease may be kept in check by 
spraying with a standard fungicide. 

Blight 

Caused by Fhyllosticta primuUcola Desm. 

Symptoms. On the leaves of the plant appear 
somewhat circular spots (fig. 63, b) that are brown 
or whitish in color with a light border, with which 
are found numerous pycnidia. The disease attacks 
various species of the genus Primula with different 
effects. On P. sieboldii and on P. obconia, the trouble 
is usually confined to the lower leaves. On P. 
sinensis the central part of the leaf is attacked be- 
fore the surrounding tissue loses its color. On P. 
sieboldii the leaves may often be blotched through- 
out, while on P. obconia one-half of the leaf is 



[ 

Primrose Diseases 317 

often destroyed before the other half shows any- 
marked deterioration. 

Little is known of the causal organism. The de- 
struction by fire of diseased material and spraying 
with a standard fungicide is recommended. 

Leaf Spot 

Caused by Ascochyta primulcz Wail. 

Symptoms. The presence of the disease is shown 
by oval spots, which spread and often involve the 
entire leaf. This disease may often be mistaken 
for the spotting caused by Phyllosticta primulicola. 
However, a microscopical examination will distin- 
guish the two organisms. 

Leaf Blotch 

Caused by Ramularia primul^z Thun. 

Symptoms. The presence of the disease is shown 
by large yellow blotches in the ashen colored cen- 
ters of which are borne the spores (fig. 63, d.). 

The Organism. The conidiophores grow on both 
sides of the spots, and are rarely branched, con- 
tinuous and somewhat denticulate. The conidia are 
thick but taper towards both ends. Their structure 
is continuous or one septate. 

Control. This disease may be kept in check by 
spraying the plants with a standard fungicide. In- 
fected material should be destroyed by fire. 



3i8 Diseases of Greenhouse Crops 



Roses {Rosa gallica chinensis) . 

Cultural Considerations, As soon as the cut- 
tings form roots which are about one-half inch in 
length, they should be potted. At this stage, if 
left too long in the propagating bench, the wood 
tissue of the cutting will harden and the subsequent 
health of the plant will be endangered. A medium 
water-holding capacity is an indication of a good 
potting soil for roses. Most greenhouse (ng. 64) 
varieties prefer a heavy loam. Other varieties such 
as the Maryland thrive best in a soil which contains 
a large percentage of sand. Roses are very sensi- 
tive and readily become injured when given partly 
decayed organic matter. The case, however, is dif- 
ferent when well rotted manure is used, for this 
latter food exerts a wholesome stimulating effect. 
The development of a good root system largely de- 
pends on the soil texture and on the plant food which 
it contains. It is necessary to stir frequently the sur- 
face soil of rose benches. This not only destroys 
weeds, but also provides aeration. However, as 
soon as the surface soil becomes filled with feeding 
rootlets of the rose plants, the cultivating should be 
done very superficially or should cease altogether. 
During active growth, the plants require an abun- 
dance of ventilation and a comparatively low 
temperature. 

Diseases of the Rose 
Greenhouse roses are subject to the attacks of 
several important diseases. 




Fig. 64. Rose House. 



Rose Diseases 



319 



The Bronzing of Leaves 
Cause, Physiological. 

Symptoms, This trouble commonly affects 
grafted varieties of the Tea, Bride, and Brides- 
maid. By some growers the disease is often mistaken 
for a stage of the black spot caused by Diplocarpon 
rosiZ. Bronzing produces a mottled bronze color- 
ing of the foliage. Later the mottling becomes 
more prominent in the form of spots, while the ad- 
joining tissue turns pale yellow. Frequently the 
entire leaflet becomes bronzed with no yellowish 
color apparent. At times the affected leaflets and 
leaf stalks drop to the ground. The cells of the 
affected tissue contain an abundance of calcium oxa- 
late crystals, a condition that indicates poor nutri- 
tion. Bronzing is usually confined to two places. 
First, where a stem has been cut and a new branch 
has started the leaf at the base begins to bronze; 
second, where an eye or an auxiliary bud has been 
rubbed off, the leaf generally becomes bronzed. 
From studies made at the Massachusetts Station* 
there seems to exist a difference in susceptibility 
between young and old plants. Bronzing may be 
expected to occur on young plants. It is also prev- 
alent both on plants which are forced too rapidly 
and on weak stock. The selection of strong, hardy 
stocks and care in feeding will prevent the trouble 
from becoming serious. 

♦Massachusetts Agr. Expt. Sta. (Hatch) Ann. Rept.: 156-159, 
1899. 



320 Diseases of Greenhouse Crops 



Blossom Blight 
Cause, unknown. 

Symptoms, The trouble manifests itself in the 
failure of the buds to open. At first the buds 
seem to develop normally. Soon, however, the 
outer petals wrinkle, turn yellow or straw colored, 
and stop growing. Occasionally the buds open par- 
tially, but fail to attain normal size. The true cause 
of the disease is unknown, although, as believed by 
Stevens and Hall,* it may be due to some physio- 
logical disorder in the metabolism of the plant. 
No control method is known. 

Crown Gall 

Caused by Pseudomonas tumefaciens Sm. and 
Towns. 

This disease is a very dangerous enemy to out- 
door roses. It has, however, proved of little eco- 
nomic importance to indoor roses (fig. 65, b.). 
For a description of the symptoms and of the or- 
ganism, see p. 1 15. 

Downy Mildew 

Caused by Feronospora spars a Berk. 
Symptoms. Downy mildew is more difficult to 
detect than the powdery mildew. It is also more 

* Stevens, F. L., and Hall, J. G., North Carolina Agr. Expt. 
Sta., Thirty-first Ann. Rept.: 78-79, 1908. 



Fig. 65. Rose Diseases. 

a. Piloboltis crystallinis (i) Group of sporophores, (2) specks on leaf, ("3) 
method in which the spore bearing cap is blown off, (4) spore head magni- 
fied, (5) yonng sporophore (after Clinton), h. crown gall, c. Phragmidium sub- 
corticum (after Smith, R. E.), d. powdery mildew. 



Rose Diseases 



321 



difficult to control, because the causal organism 
lives within the tissue of its hosts. This mildew 
resembles that of the grape, potato, bean, etc. It 
usually appears in irregular spots. On the lower 
surface of the leaves, the fruiting of the fungus 
resembles a downy white to purple coating. It is 
fortunate that this disease is uncommon in the 
United States, and even more so under greenhouse 
conditions. 

The Organism. The conidiophores are nine 
times branched; the branchlets are reflexed. The 
conidia are pale gray, subelliptic in form. 

Control, The removal and burning of infected 
material and the spraying of the plants with a stand- 
ard fungicide will keep it in check. 

Mechanical Spotting 

Caused by Piloholus crystallinus (Wigg.) Tode. 

Symptoms. The trouble, if such it may be called, 
is a small specking resembling fly speck on the 
leaves and flowers. There is but one case on record 
reported by Clinton.'^ It appeared on two benches 
in a rose house. The infected benches were heavily 
mulched with cow manure, while the others did not 
receive this treatment. A careful inquiry revealed 
the fact that on the two manured beds the fungus 
Filobolus crystallinus was very abundant. The 

* Clinton, G. P., Conn. Agr. Expt. Sta., 38th Ann. Rept.: 24-25, 
1914. 



322 Diseases of Greenhouse Crops 

spore heads of this organism (fig. 65, a) when ripe 
are shot off into the air and stick to any object on 
which they may alight, which in this case happened 
to be the foliage and blossoms of the roses. The 
mechanical spotting here referred to was caused by 
nothing more than the presence of the spore heads 
of the fungus. The trouble ceased when the fungus 
no longer produced spores. The specking on the 
rose blossoms was not serious enough to injure their 
market value. 

Rose Rusts 

Caused by Phragmidium species. 

Rose rusts are more commonly found on plants 
growing in the open. These, however, may be intro- 
duced indoors with cuttings, or plants first started 
in the nursery. 

Fhragmidium suhcorticum (Schrank) Wint. 
This fungus causes the true rust of roses. It is Ytrj 
prevalent in Europe, is of little importance in the 
United States. On the leaves this rust appears in 
small circular spots (fig. 65, c), and on the stems 
and petioles in large powdery masses. At first the 
sori or spore clusters arc orange-yellow, but later 
turn brick red. 

Phragmidium speciosum Fr. This fungus is the 
cause of a rose rust which affects the stems and 
which rarely appears on any other part of the plant. 
The sori are black and irregularly scattered. The 
causal fungus is carried over from year to year as 
viable mycelium in the affected host. Cutting out 



Rose Diseases 



323 



or burning the diseased stems will prevent the fur- 
ther spread of the disease. 

Other Rose Rusts, There are other species of 
Phragmidiums which have been found by Mikio 
Kasai.''* Among them are the following: Phrag- 
midium americanum (Pk.) Diet, found on Rosa 
dahierica; Phragmidium fusiforme Schroet on Rosa 
acicularis; Phragmidium Japonicum Diet, on Rosa 
multiflora, R. wichuriana, R. lucise; Phragmidium 
rosdd multiflora Diet, on Rosa multiflora, R. laevi- 
gata; Phragmidium rosa rugoscz Kasai, on Rosa 
rigosa; Phragmidium yezoense Kasai on Rosa 
rugosa. 

Powdery Mildew 

Caused by Spharotheca pannosa Wallr. 

Symptoms, Powdery mildew is a very trouble- 
some disease of greenhouse roses. The disease ap- 
pears as powdery, whitish patches on the leaves, 
stems, and blooms. The affected foliage fails to 
develop normally, becoming uneven and twisted, 
curled and reddened (fig. 65, d.). 

The Organism, On the rose the conidial or 
oidium stage is most frequent. The conidia are 
ovid, hyaline, and are borne on short conidiophores. 
The same fungus also causes the powdery mildew 
of the peach, in which case the ascus stage is most 
common. 

Control, It is believed by many florists that 

♦Mikio Kasai, Trans. Sapporo Nat. Hist. Soc. 3: 27-51, 1909- 
19 10. 



324 Diseases of Greenhouse Crops 



drafts favor mildew. These statements seem to be 
borne out by actual observ^ations. Mildew often 
starts first on rose plants facing broken panes. From 
these, the spores are then carried by the draft to 
other plants until the disease becomes thoroughly 
established in the house. It is, therefore, impera- 
tive that attention be directed to broken glass. 
While an abundance of ventilation is necessary, 
drafts of all sorts should be avoided. 

Mildew may also be kept in check by boiling 
sulphur in the greenhouse for two to three hours, 
twice a week. The house is closed tightly during 
the operation, and ordinary flowers of sulphur is 
placed in a kettle over a small kerosene flame, as 
otherwise a big flame may cause the sulphur to catch 
fire. Mildew may also be controlled by spraying 
with potassium sulphide, at the rate of one ounce 
of the chemical dissolved in two gallons of water. 
The spray is only effective when used fresh. The 
chemical should be kept in a tightly closed bottle. 

Black Spot 

Caused by Diplocarpon ros(Z Wolf. 

Symptoms. Black spot is often very troublesome 
on greenhouse roses. Attacked plants lose their foli- 
age and the general effect is a weakening of the 
plant and the fonr.ation of stunted blossoms. The 
spots are more or less circular, black, with a char- 
acteristic fringed border (fig. 66, a.). Frequently 
the leaf tissue adjacent to the spots becomes pale or 



Fig. 66. Rose Diseases. 



a. Black spot on foliage, b-g. various stages of 
Diplocarpon rosa (after Wolf), h. Septoria rosic 
(after New Zealand Ann. Rept., 1915)- 



Rose Diseases 



325 



chlorotic, long before the affected leaves drop off. 
As the spots become old, minute specks appear 
within. These are the fruiting bodies of the causal 
organism. 

The Organis7n, The fungus of black spot has two 
spore stages. The summer stage (fig. 66, b) is 
known as Actinone??ia roscz (Lib.) Fr. The pycnidia 
are tuberculoid in shape, scattered, black. The co- 
nidia (fig. 66, c) are oblong, constricted, and are 
borne on short conidiophores. The ascus or winter 
stage (fig. 66, f and g) was discovered by Wolf,* 
who named it Diplocarpon roscz Wolf. The winter 
stage matures on dead and fallen leaves which have 
wintered over. The mature asci are oblong. The 
ascospores are discharged from an apical pore and 
pile up in whitish masses in the opened perithecia. 
The ascospores are not so strongly constricted at the 
septum as is the case with the conidia or summer 
spores, both of which are hyaline in color. 
' Control, There seems to be a difference in the 
susceptibility of som^e varieties to the disease. It 
seems that the bushy sorts are m.ore susceptible than 
the climbing varieties. The thin-leaved varieties, 
too, seem to possess less resistance than those with 
' thick leaves. 

Spraying is often recommended for the control of 
black spot. The more recent investigations by 
Massey t show that ammoniacal copper carbonate 
is not as efficient as Bordeaux mixture for the con- 

*Wolf, F. A., Science N. S. 35: 151, 1912. 

t Massey, L. M., The American Rose Mann: 67-71, 1918. 



326 Diseases of Greenhouse Crops 



trol of the disease. Furthermore, the disease may 
be kept in check by dusting with sulphur-arsenate 
made of a mixture of ninety parts finely ground 
sulphur and ten parts powdered arsenate of lead. 
A lime sulphur solution composed of one part of 
the commercial concentrate solution to fifty parts 
of water is as efficient in controlling black leaf spot 
as is Bordeaux or sulphur-lead-dust. It is purely 
for the florist to decide whether he wishes to spray 
or to dust. The sulphur-arsenate may be applied 
with an efficient little machine known as the Corona 
hand duster. The same material is also very effi- 
cient for controlling the powdery mildew of the 
rose. In this case, too, the work of Massey has 
shown that sulphur-arsenate is even more efficient 
than lime-sulphur solution 1-50, or Bordeaux mix- 
ture 5-5-50. 

Anthracnose 

Caused by Glceosporium roscz Hals. 

Symptoms, The chief feature of this disease as 
observed by Halsted is a premature dropping of 
the foliage. Some stems may be entirely bare while 
others may have a few leaves still clinging to them. 
Infection may start on the leaves first, in which case 
they drop off, and soon develop the salmon-colored 
pustules on the dead spots. Generally, however, 
the trouble starts at the tender branches and works 
its way downwards. If infection takes place at a 

♦Halsted, B. D., New Jersey Agr. Expt. Sta., Fourteenth Rept.: 
401-409, 1893. 



Rose Diseases 327 



lower portion of the cane it will soon work its way 
up. The characteristic salmon-colored pustules are 
usually found in abundance on the affected canes. 
The rose anthracnose is very similar to that of the 
raspberry, although the latter is induced by a differ- 
ent species of fungus. Very little is known of the 
causal organism of the rose anthracnose. 

Control, All dead leaves and canes should be re- 
moved and destroyed by fire. Spraying with a 
standard fungicide is also recommended. 

Leaf Spot 

Caused by Mycosph^rella rosignea (E. and E.) 
Lind. 

Symptoms, Purplish blotches appear on the 
leaves and later develop into sharply defined spots 
with brown centers and purplish borders. The peri- 
thecia of the fungus are found in large numbers on 
the dead tissue. It seems that the one-year-old 
plants are more susceptible to the disease than the 
two-year-old plants of the same variety. The dis- 
ease usually occurs in the winter, but seldom causes 
serious damage. 

The Organism, The perithecia are black and 
partly erumpent, while the asci are rather oblong 
and are arranged in two series in the ascus. 

Control. The destruction by fire of all diseased 
material, and spraying with a standard fungicide is 
recommended. 



328 Diseases of Greenhouse Crops 



Septoria Leaf Spot 

Caused by Septoria roscz Desm. 

Symptoms. This disease is characterized by dis- 
tinct spots on the foliage (fig. 66, h.). Spots 
with centers of creamy or dirty white surrounded 
by broad purple margins appear on the foliage. The 
pycnidia are formed in the center of the spots. Lit- 
tle is known of the nature of the causal organism. 
The destruction of all infected material by fire and 
spraying with a standard fungicide will keep the 
disease in check. 

Stem Canker 

Caused by Coniothyrium fuckelii Sacc. 

Symptoms. This disease usually produces cankers 
of the canes and branches. The lesions are brown 
in the center with a black border, limited by an out- 
ward reddish band or zone. The same disease at- 
tacks apples and raspberries. 

The Organism. It has long been suspected that 
Leptosphseria was the ascus stage of Coniothyrium 
fuckelii. This Stewart seems to have verified, 
although definite evidences are still lacking. The 
perithecia are in groups, globose, black with fringed 
mouths. The asci are cylindric, eight-spored, one- 
rowed, three-septate. The pycnidia are similar to 
the perithecia; the spores are ovate, continuous, and 

♦Stewart, F. C, New York (Geneva) Agr. Expt. Sta. Bui. 328: 
387, 1910. 



Rose Diseases 



329 



grayish. Careful cutting and burning of affected 
material is suggested. 

The Crown Canker 

Caused by Cylindrocladium scoparium Morgan. 

Symptoms. Crown canker is perhaps one of the 
most important diseases of roses under glass. Al- 
though the percentage of roses that are actually 
killed is rather small the effect of the disease is to 
increase the financial loss by weakening the plants 
and reducing the yields in marketable blossoms. The 
disease first attacks the plants at the crown just 
above the surface of the soil, producing lesions both 
on the crown and on the roots. Infection often 
starts at the place of union of the scion and stock. 
The trouble is indicated by a slight discoloration of 
the bark, which soon deepens until the affected tissue 
becomes black and watersoaked (fig. 67, b.). As 
the lesions increase in number, the crown of the 
plant becomes girdled, and cracks appear in the 
bark of the infected area, which is sunken and in 
sharp contrast with the healthy bark surrounding it. 

Another constant symptom of the disease is the 
punky consistency of the affected tissue. Although 
this effect is marked in the crown, especially of the 
diseased roots, the condition is further noticeable 
in the bark and sap wood of the affected crown or 
roots. The diseased roots send up suckers that are 
weak, spindly, and pale. A close examination will 
show that these, too, are affected at the point of 



330 Diseases of Greenhouse Crops 



attachment to the root. Affected plants linger for a 
long time, but they produce only a few stunted 
blossoms. 

The Organism. The causal organism produces 
fertile and sterile hyphse. The spores are borne in 
fascicles, are cut off from the short conidiophores 
by a constriction, and are held together by a sticky 
substance, but separate quickly when placed in 
water. The spores are cylindric, one septate, and 
hyaline (fig. 67, c to e.). 

Control. Since the causal organism lives in the 
soil, steam sterilization is recommended. All dead- 
or infected material should be destroyed by fire. 
The disease may also be avoided to some extent 
by placing grafted plants with the graft union above 
the soil. This will prevent infection at the wounded 
surface. Attention should also be given to the 
watering of the plants. Crown rot is worse in over- 
watered beds. 

Cercospora Leaf Spot 

Caused by Cercospora rosicola Pass. 

Symptoms. This disease is characterized by 
roundish spots, gray in color, with a dark border 
separating the health)^ from the diseased tissue. 

The Organism. The conidiophores grow in tufts, 
are densely gregarious, small and dark colored. 
Conidia are straight, short, cylindric, and hyaline. 
Spraying with a standard fungicide is recommended. 




Fig. 68. Rubber Plant and Schizanthus 
Diseases. 

a. Leptostromella leaf spot, b. cross section of rubber 
leaf to show relationship of the parasite to its host, to 
the left one magnified spore (after Hatch Expt. Sta. 
9th Rept. 1897), c. and d. acervulus and germinating 
spores of Colletrotrichum schizanthi Jen (after Jensen, 
C. N.). 



Rubber Plant Diseases 331 



The Rubber Plant {Ficus elasticd) 

Cultural Considerations, Rubber plants generally 
adapt themselves to wide ranges of temperature. 
They may do as well when exposed to full sunlight 
as when kept under partial shade. In the summer 
it is advisable to plunge them out of doors to be 
hardened. The plants require frequent feedings with 
liquid manure. 

Diseases of Rubber Plants. 

The rubber plant is considered very hardy. It is 
subject to but few diseases of importance. 

Leaf Spot of India Rubber 

Caused by Leptostromella elasticcz Ell. and Ev. 

Symptoms, The India rubber (Ficus elastica) is 
usually considered a hardy plant. Under green- 
house conditions, however, it is often attacked by a 
leaf spot which at times proves very disastrous. The 
presence of the disease is first manifested by small 
spots (fig. 68, a) or streaks. These soon increase 
in number and in size until the entire leaf area 
becomes involved, resulting in a premature dropping 
of the foliage. The spots, which at first appear yel- 
lowish, soon turn brownish and finally become gray. 
The dead tissue is sharply defined from the living 
as it is banded by a narrow black margin. The 
pycnidia (fig. 68, b) appear scattered within the 



332 Diseases of Greenhouse Crops 



spots. The pycniospores are oblong, hyaline, and 
one celled. 

Control, All dead and infected leaves should be 
destroyed by fire, and the plants should be sprayed 
with ammoniacal copper carbonate. 

ScHizANTHus {Schzzantkus pnnatus) 

Cultural Considerations. Schizanthus is forced 
mostly as an early spring flower. It does not require 
a very rich soil, and thrives best under night tem- 
peratures of 45 to 50 degrees F. 

Diseases of Schizanthus. 

Schizanthi are very hardy plants. There is but 
one disease recorded in the United States on the 
greenhouse plants. 

Anthracnose 

Caused by Colletotrichum schizanthi Jen. and 
Stewart. 

Symptoms. Anthracnose has been found by Jen- 
sen and Stewart* to be a very destructive disease on 
greenhouse Schizanthus. The younger parts of the 
plant are usually more susceptible than the older 
ones. On infected stems, branches, or petioles, the 
disease causes watersoaked areas which extend in all 
directions. The spots become depressed, and grow 

♦Jensen, C. N., and Stewart, V. B., Phytopath i: 120, 1911. 



Schizanthus Diseases 333 



deeper and deeper until the affected parts topple 
over and break. The lesions are light brown and 
dotted with the acervuli of the fungus. On the older 
parts of the plant the lesions take on the forms of 
cankers, although they do not sink as deeply. Oc- 
casionally, the disease attacks the leaves, forming 
light brown spots which are irregularly scattered. 

The Organism, In structure Colletotrichum 
schizanthi is not different from any other Colleto- 
trichum. The black setae are very numerous. The 
conidia are one celled, hyaline, oblong, and granu- 
lar (fig. 68, c and d.). 

Control. Diseased plants or parts of plants 
should be destroyed by fire. Spraying with a stand- 
ard fungicide is also recommended. 



CHAPTER 26 



THE SWEET PEA {Lutkyrus odoTdtus L.) 

Cultural Considerations.^ The best position 
for a sweet pea house (fig. 69, a) is east and 
west with a full southern exposure. The sides of 
the house should be considerably higher than for 
other crops. Sweet peas require an abundance of 
water during the growing season. Frequent syring- 
ing of the foliage is also necessary to keep the red 
spider in check. In ventilating care should be taken 
not to admit cold drafts; nor should the plants ever 
be chilled. Exposure to drafts or sudden falls in 
temperature will predispose the plants to bud drop 
and to powdery mildew. 

Diseases of the Sweet Pea 

Indoor sweet peas are subject to numerous dis- 
eases. These, if allowed to spread, will deprive the 
grower of his year's labor and profits. 

Physiological Troubles 

These troubles are usually induced by improper 
conditions of the soil. Root burn, for instance, may 

* For fuller information see Taubenhaus, J. J. Culture and 
Diseases of the Sweet Pea, 1917. E. P. Dutton Co., New York, N. Y. 

334 




Fig. 69. Sweet Pea Diseases. 

a Ranch of sweet pea houses, b. sick soil infected with Sclerotinia liber- 
tiana; notice the wilting and dying of the seedlings, c. some of the same soil 
steam sterilized resulting in a perfect stand, d. germinated sclerotia showing 
fruiting caps of 5". libertiana. 



Sweet Pea Diseases 335 



be induced by the excessive use of wood ashes ap- 
plied with the manure. It is not uncommon for 
growers to use wood ashes at the rate of 1,500 lbs. 
to 4,500 square feet of bed space. This would be 
equivalent to nearly seven and one-half tons per acre. 
Under such conditions the roots actually bum up 
because of the strong alkalinity of the soil. More- 
over, hard-wood ashes contain about 30% caustic 
lime and from 5 to 12% potash. Both of these ele- 
ments in excess in soil render it too alkaline for plant 
growth. To remedy this trouble, acid phosphate is 
used, followed by a good drenching with water. This 
will help to neutralize the alkalinity and to restore 
the balanced ration. 

Malnutrition 
Cause, physiological. 

Symptoms. The symptoms of malnutrition of 
sweet peas a-re identical with those of greenhouse 
cucumbers (see p. 134). 

Cause. Overfertilization may be mentioned as 
one of the many causes of malnutrition. An analy- 
sis of an overfed soil will readily show that the solu- 
ble salts present are in excess of what the plant re- 
quires and is able to withstand. Table 17 a by 
Haskins clearly shows that with the exception of 
nitrogen, the soluble salts were in excess of what the 

♦Haskins, H. D., Mass. Agr. Expt. Sta., Twenty-fifth Ann. 
Kept.: 76-79» 1913- 



336 Diseases of Greenhouse Crops 

Table 17 a 



Average Composition of an Overfed Soil Com- 
pared to a Normal Soil 





Pounds per Acre 




Normal 


Overfertilized 




Soil 


Soil 




12.874 


15- 193 


Soluble nitrogen 


209 


91 


Soluble potash 


2.433 


2.957 


Soluble phosphoric acid 


traces 


traces 


Soluble calcium oxide (lime) 


580 


657 




369 


435 




972 


1.923 









plant could stand. It further indicates that a large 
amount of horse manure was used in this particular 
case. 

Control. It seems that the average greenhouse 
beds are faulty in construction. One of the main 
requisites is to provide good drainage. This is far 
more important in the greenhouse than in the open. 
Crops need plant food. A slight excess is desirable 
to force quick growth. An overdose of horse ma- 
nure or chemical fertilizers will produce more harm 
than good. No guesswork should be permitted to 
take the place of accurate calculation in applying 
fertilizers. The surface area of the greenhouse bed 
may be easily expressed in terms of acreage. Sup- 
pose that 500 pounds of sulphate of potash is re- 
quired per acre (4,800 square yards), then in the 
greenhouse 1.6 ounces would be required per square 
yard. In this way, all fertilizers may be applied 



Sweet Pea Diseases 337 



accurately. In relying on guesswork the general re- 
sults are likely to be the application of an overdose 
of fertilizers or manure. 

In order to gain an approximate idea of the total 
amount of plant food as well as the available plant 
food furnished by horse manure when mixed with 
the soil for greenhouse use, Haskins has prepared 
the following data: 





Pounds of Total 
Plant Food per Acre 


Pounds of Plant Food 
Likely to he Available 
the First Season 




A* 


B* 


C* 


A* 


B* 


C* 


Nitrogen 


5.800 


3 863 


2.900 


2.320 


1-545 


1 . 160 


Phosphoric acid 


2.800 


1.850 


1 .400 


2.380 


1.585 


1. 190 


Potash 


5 300 


3 530 


2.650 


3.971 


2.648 


1.985 



*"A" represents one-half manure, one-half soil; "B", one-third 
manure and two-thirds soil; "C", one-fourth manure and three- 
fourths soil. 



In greenhouses when the ill effects of overfertili- 
zation become apparent, the soil should be leached 
out with hot water as soon as the crop is removed. 
This may also be done with lukewarm water, while 
the crop is still growing. In either case good drain- 
age should always be provided in order to carry off 
the salts in solution. Where conditions for leaching 
are not favorable as may be the case with a cucum- 
ber crop, about 3 inches of fresh loam should be ap- 
plied to the surface of the bed and thoroughly 
worked in. 



338 Diseases of Greenhouse Crops 



Bud Drop 

As the name implies, the young flower buds at a 
very early age turn yellow and drop off. This drop 
should not be confused with the drop produced by 
the anthracnose disease. In the latter case, the 
flower develops into a normal spike but it is at- 
tacked soon by the fungus Glomerella rufomaculans 
which girdles it at the point of attachment between 
the flower and the peduncle. Here the flower often 
drops off, leaving behind the beheaded peduncle. In 
the former case, however, the minute young flower 
bud never develops, instead it turns yellow and drops 
off. There seems no doubt that the drop is a physi- 
ological disease and is induced by an unbalanced con- 
dition of the food elements in the soil. This may 
occur in a soil that has been excessively fed or in a 
soil that is lacking in plant food. 

Bud drop may be readily remedied by the appli- 
cation to the soil of small quantities of muriate of 
potash and acid phosphate. 

Mosaic, see p. 102. 
Streak 

Caused by Bacillus lathyri Manns and Taub. 

Streak is a very serious disease of outdoor sweet 
peas. Fortunately it is not known to attack green- 
house sweet peas. 

Symptoms. Although not occurring indoors, the 



Sweet Pea Diseases 339 



symptoms of streak are here given to enable the 
grower to know the disease should it ever appear in 
the greenhouse. Like the Bacteriosis of beans, streak 
makes its appearance in wet houses. On the sweet 
pea the disease usually appears just as the plants 
begin to blossom. It is manifested by light reddish- 
brown to dark brown spots and streaks (the older 
almost purple) along the stems, having their origin 
usually near the ground, indicating the fact that the 
distribution of the disease is by the spattering of 
water droplets and soil particles, and that infection 
takes place through the stomata. The disease be- 
comes quickly distributed over the more mature 
stems until the cambium and deeper tissues are de- 
stroyed in continuous areas, whereupon the plant 
dies. Occasionally petioles and leaves show infec- 
tion; the latter exhibiting the usual water-soaked 
spots and resembling the bacterial leaf blight of 
beans. 

The disease is not a vascular infection ; it confines 
its attacks to the mesophyll, the cambium and deeper 
parenchymatous tissues. The lesions of the stems 
gradually enlarge and deepen until they come to- 
gether. 

Downy Mildew 

Caused by Peronospora trifoliorum De By. 

Symptoms, This trouble usually makes its ap- 
pearance when the plants are a few inches high or 
it may attack older plants. Affected leaflets become 



340 Diseases of Greenhouse Crops 



sickly yellow, finally white, shrivel and die, show- 
ing but very little of the fruitings of the causal 
organism on the surfaces of the affected areas. Un- 
der very moist conditions, however, the spots become 
covered with a delicate grayish lilac colored moldy 
growth. The latter consists of the summer spores 
of the fungus. The winter or resting spores are 
found imbedded in the dead tissue of the host. Mas- 
see * claims that downy mildew is a serious disease 
of outdoor sweet peas in England. Although the 
fungus Peronospora trifoliorum is wtry common on 
other legumes in the United States, it has not yet 
made its appearance on the sweet pea. Mr. Massee 
says that Peronospora vici(Z Berk, also attacks sweet 
peas in England. 

Stem or Collar Rot 

Caused by Sclerotinia lihertiana Fckl. 

Symptoms. This is usually a seedling disease, al- 
thtDugh it may attack plants of all ages. Like the 
Rhizoctonia rot, it attacks many different kinds of 
seedlings. The trouble is most severe in poorly ven- 
tilated houses in beds overwatered or lacking proper 
drainage, and in damp places out of doors. The 
disease spreads very quickly and is soon fatal. Af- 
fected plants first show a wilting of the tip and a 
flagging of the leaves, and then the seedlings fall 
over and collapse (fig. 69, b.). The causal fun- 
gus does not seem to attack the roots, but penetrates 
the collar of the stem and completely invades the 

♦Massee, G., Sweet Pea Annual: 20-21, 1906, London 



Sweet Pea Diseases 341 



vessels, thus clogging the upward flow of the water 
from the roots to the stem. Freshly collapsed 
plants usually have a water-soaked appearance, and 
are later overrun by a white weft, which is merely 
the mycelium of the fungus; this is followed by 
sclerotia (fig. 69, d) (resting bodies), which are 
found scattered here and there on or within the af- 
fected stems. The fungus is a soil organism which 
occasionally causes trouble in clover fields. It is in- 
troduced with animal manure. For a description of 
the causal organism and methods of control, see p. 
151. 

Thielavia Root Rot 

Caused by Thielavia hasicola Zopf. 

Symptoms. Plants severely infected with Thie- 
lavia develop practically little or no root system, 
since the new roots are destroyed as soon as they are 
formed. Generally all that is left is a stub, which 
is charred in appearance (fig. 70, b.). The dis- 
ease often w^orks up from the affected roots to the 
stems, some 2 or 3 inches above ground. Affected 
plants neither die nor wilt, but remain dwarfed, 
stunted, and sickly pale in color, and produce few 
or no blossoms. For a description of the causal or- 
ganism and methods of control, see p. 355. 

Powdery Mildew 

Caused by Microsphera alni (Waller) Salm. 
Symptoms. Powdery mildew is a very common 
trouble of greenhouse sweet peas. The causal fun- 



342 Diseases of Greenhouse Crops 



gus grows on the surface of the leaves in powdery 
white patches. Affected leaves become pale and 
drop off prematurely. The ascus stage of Micro- 
sphera almi is rarely found on the freshly affected 
foliage. It is, however, fairly abundant on the dead 
and fallen leaves on the ground. The mildew may 
be controlled in the same manner as for the rose 
(see p. 323). 

Spot Disease 

Caused by Mycospharella pinodes (Berk, and 
Blox.) Niesel. 

Symptoms, Although it is a dangerous enemy of 
the garden pea, this disease has not attacked sweet 
peas very often, especially where they are grown 
under greenhouse conditions. The pycnidial stage 
of the fungus is found on foliage of the garden pea 
and of the sweet pea. The winter stage may be 
found on dead leaves and vines of the sweet pea 
and of the garden pea. 

The Organism. The pycnidia are brown, erum- 
pent, globose, with thin walls. The spores are hya- 
line, cylindrical, one septate and rounded at both 
ends; they are guttulate only when young. The 
perithecial stage was discovered by Stone. The 
brown perithecia are found under the epidermis or 
deeply sunken in the tissue of the spot. Their mouths 
are elongated and beaklike. The asci are cylindri- 
cal, while the ascospores are elliptical to ovate. Both 
are two-celled hyaline bodies. Spraying with a 
standard fungicide may keep the disease in check. 



Sweet Pea Diseases 343 



Anthracnose 

Caused by Glomerella rufomaculans (B.) V. Sch. 
and Sp. 

Symptoms, Like streak, anthracnose has not yet 
made its appearance on greenhouse sweet peas. 
Whether this is merely accidental, or whether indoor 
conditions are unfavorable to the disease remains to 
be discovered. It is necessary, however, that the 
grower be familiar with the disease in order to pre- 
vent its spread indoors. The symptoms of Anthrac- 
nose are manifested in a wilting or dying of the tips, 
which become whitish and brittle and readily break 
off. At other times the wilt works downwards and 
involves the entire branch. Frequently, also, leaves 
thus infected become brittle and soon drop (fig. 
70, a.). Examination of an infected leaf with a 
hand lens shows that it is peppered with minute 
salmon-colored pustules. At the time of blossoming 
the fungus makes its attack on the peduncle, or the 
fungus attacks both the flower bud and the peduncle, 
in which case both dry up, although they do not fall 
off. The most distinguishable symptoms of this 
disease are on the seed pods. Infected pods lose 
their green color, become shriveled, and are soon 
covered with salmon-colored patches, which cannot 
fail to attract attention. 

Organism, The cause of the anthracnose is the 
fungus Glomerella rufomaculans. This fungus 
causes also the bitter rot of apple and the ripe rot 
of grapes. Cross inoculations have definitely proven 



344 Diseases of Greenhouse Crops 



that the fungus can go back and forth from the 
apple to the sweet pea and vice versa. Anthracnose 
begins its destructive work early, even in the seed- 
ling stage. 

CHiETOMiuM Root Rot 

Caused by Chatomiu7n spirochczte Pratt. 

This disease is of minor importance. It is found 
on plants weakened by poor cultural conditions, such 
as overwatering. The symptoms of this trouble 
greatly resemble the injury from Thielavia root rot. 
The only way, however, to tell them apart is micro- 
scopically. 

FusARiuM Wilt 

Caused by Fusarium lathyri Taub. 

Symptoms, This disease is of much greater im- 
portance to greenhouse men than root rot. The 
writer has known of instances where the disease has 
ruined the entire crop of indoor sweet peas. After 
several resowings, the owners gave up in despair any 
further attempt to grow them. Florists should do 
everything to prevent the introduction of the dis- 
ease into the house. In places where this disease 
has made its appearance the growing of greenhouse 
sweet peas had to be abandoned within less than two 
years. The disease produces a sudden flagging of the 
leaves which is accompanied by a wilting and col- 
lapse of the seedlings (fig. 70, c). Usually, upon 
sowing the seed, a fair percentage germinate and 
reach a height of about eight to ten inches, when they 



Sweet Pea Diseases 345 



are attacked by the fungus. If the collapsed seed- 
lings are allowed to remain on the ground, the dead 
stems will soon be covered with the sickle-shaped 
spores of the Fusarium fungus. Eventually the dead 
tissue rots, attracting small fruit flies, which begin to 
distribute the spores to different places in the same 
house. The trouble usually appears in widely sep- 
arated spots on the bench. These spots, however, 
quickly spread, involving the entire bed, the plants 
of which may suddenly assume a wilted appearance. 
Here and there, however, and in the same bench, a 
few plants remain alive and keep on growing in 
spite of the disease. 

The Organism. The mycelium of the fungus is 
hyaline, septate, and branched. At an early age 
the hyphse begin to form chlamydospores. These are 
round hyaline bodies filled with oil globules and are, 
formed in the center of the hypha, whereupon the 
contents of the cell collects into the chlamydo- 
spores. Usually, the chlamydospores are also borne 
at the tip end of the hyphse in chains of twos, threes 
and even fours. Old cultures are practically one 
mass of chlamydospores. There are also two spore 
forms present, which appear as early as the third 
day in the pure culture. These comprise microco- 
nidia which are fairly abundant and macroconidia, 
var}dng from two, three to four celled. The aver- 
age form of macronidia is the three celled. Both 
micro- and macroconidia are hyaline and smooth. 
In old cultures the macroconidia shrink so that the 
septa become slightly pronounced. These old ma- 



346 Diseases of Greenhouse Crops 



croconidia soon lose their protoplasm or let it break 
up until it presents a granular appearance. In young 
cultures, the outer wall of the chlamydospore is 
smooth, but in old cultures it becomes slightly warty 
or covered with minute points. No perfect stage has 
been found to accompany this fungus either in pure 
culture or on the host. This disease may be con- 
trolled by the steam method of sterilization. 

Root Rot 

Caused by Rhizoctonia solani Kuhn. 

Symptoms. This trouble is of considerable impor- 
tance to greenhouse men. The disease may destroy 
the entire stand, or cause it to be uneven, thus ne- 
cessitating several resowings. Severely infected 
plants have practically no root system (fig. 71, b.). 
In less infected plants only one or two rootlets may 
be destroyed. The fungus produces a browning ef- 
fect of the root before total destruction sets in. In 
very early stages of infection the seedlings are seen 
to have a wilted appearance; as the disease pro- 
gresses the infected seedlings fall over and collapse. 
The fungus is not confined to the roots alone. It is 
often seen to work its way up the stem and produce 
a constricted area marking it off from the healthy 
part. As the fungus is a soil organism, it is usually 
introduced with manure, infection taking place at 
any part of the roots or stems. In the latter case 
reddish sunken spots are observed at the base. Root 
rot is primarily a seedling disease, although older 



Sweet Pea Diseases 347 



plants, too, may be affected. Such plants linger for 
some time but are valueless. Corticum vagum is a 
soil fungus which attacks a number of other green- 
house as well as outdoor plants. In this case, the 
organism (fig. 71, c) either produces a damping 
off among young seedlings, or deep cambium lesions 
on the stem. With sweet peas the injury is the same. 
Root rot is introduced in the greenhouse with in- 
fected soil or manure. Overwatering and a sour con- 
dition of the soil favor the disease. For a descrip- 
tion of the causal organism and method of control, 
see p. 20. 

Root Knot or Nematode 

Caused by Heterodera radicicola (Greef) Muller. 

Symptoms, The disease is characterized by swell- 
ings on the roots (fig. 70, d.). These are either 
small swellings formed singly, in pairs, or in strings, 
thus giving the affected root a beaded appearance. 
Again, the swellings may be very large so as to be 
mistaken for root nodules. However, these galls 
cannot be mistaken for the normal root nodules, be- 
cause the latter are lobed and are attached at one 
end, whereas the root gall produces a swelling of the 
entire surface of the part affected. Infected plants 
usually linger for a long time, but they can be dis- 
tinguished by a thin growth and yellow, sickly look- 
ing leaves and stems. The disease is introduced with 
infected manure or with compost. For a description 
of the causal organism and methods of control, see 
p. 23. 



CHAPTER 27 



TULIPS (Tulipa suaveolens gesneriana) 

Cultural Considerations. Indoor tulips are grown 
in much the same way as hyacinths (see p. 266). As 
blossoms appear, they should be put under partial 
shade. The petals are very delicate and are subject 
to burning or wilting when exposed to direct sun- 
light. 

Diseases of the Tulip 
Tulips are subject to few but serious diseases. 

Blindness 

Cause, unknown. 

Blindness in tulips is a trouble which results in 
a failure of apparently normal bulbs to produce 
flowers (fig. 72, a.). A blind tulip is distinguished 
from a normal plant by having a leaf scale only. 
This condition is prevalent where bulbs of small size 
are used. The cause of blindness, which is being in- 
vestigated by Stout,* is still undiscovered. Tulip 
bulbs which have bloomed well the previous year 
may become blind the second season. These same 
bulbs, however, may again bloom the third season. 

♦Stout, A. B., Jour. Hort. Soc. of New York 2: 201-206, 1917. 

348 




Fig. 72. Tulip Diseases. 

a. Tulip blindness, b-e. Botrytis rot. 



Tulip Diseases 349 



Thi? would seem to indicate that blindness does not 
nece. /warily mean run-down bulbs. It is very likely 
that the treatment during the curing, storage, or 
planting to a certain extent predetermines blindness. 

Smut 

Caused by Ustilago tulips (H.) Wint. 

Like the tulip rust, the smut is of little or no eco- 
nomic importance. Very little is known about either 
the disease or the causal organism. 

Rust 

There are two kinds of rust on tulip leaves. Each 
of these is caused by two species of Puccinia, namely, 
P. tulips Schw. and P. prostii. Very little is known 
of these rusts; fortunately, also, they are of little 
economic importance. 

Bulb Rot 

Caused by Sclerotinia parasitica Massee. 

Symptoms, The rot seems to be confined to the 
scales of the bulb only. The plate as well as the 
roots remains unaffected. When a tulip bulb is cut 
open, the scales are found to be more or less soft- 
ened, grayish, water-soaked, and the inner part to be 
more or less rotted. As the rot progresses, the outer 
scales become covered with a mold which forms olive 
brown, velvety patches (fig. 72, b.). This is made 



350 Diseases of Greenhouse Crops 

up of the summer spores of the fungus. Late , the 
outer scales become covered with smiall hard f mgus 
bodies, sclerotia (fig. 72, d.). Besides the tUi.jJ, the 
same disease may also attack Narcissus pseudo-nar- 
cissus, Galanthus nivalis, and Crocus vernus. 

The Organis7?i, The causal organism has two 
spore stages, the summer stage, Botrytis parasitica 
Cavara (fig. 72, c), and the winter or ascus stage, 
Sderotinia parasitica Massee.* 

Control, Since the causal organism is introduced 
with the soil, steam sterilization of the latter is rec- 
ommended. All infected material should be de- 
stroyed by fire. Care should be given to the water- 
ing and ventilation. 

ScLEROTiuM Rot 

Caused by Sclerotium tuliparum Kleb. 

The rot of tulip bulbs which is caused by the 
above organism has not as yet attained economic 
importance in this country. Very little is known of 
the disease or of the causal organisms. Hopkins f 
states that the sclerotia of Sclerotium tuliparuin are 
much larger than those of Botrytis parasitica^ the 
latter of which are small, the size of a pin head. 

Sclerotium Rot, 

Caused by Sclerotium tulip cz Lib. 

This trouble was found by Seaver + on out-of- 

*Massee, G., A Text-book of Plant Diseases: 158-159, 1903 
(London). 

t Hopkins, E. F., Phytopath. 8:75, 1918. 

X Seaver, F. L., Jour. N. Y. Bot. Gard. 18: 186-188, 1917. 



Violet Diseases 351 



doors tulips. It is doubtful whether it will prove a 
serious drawback in the greenhouse. The causal fun- 
gus causes a rotting of the bulbs, and seems also to 
be involved in at least one form of blindness. In 
the latter case, the fungus is found on the young bud 
which fails to develop and finally rots off. It is very 
probable that Sclerotium tulipcz Lib., 5. tuliparum 
Kleb., and S. bulborum^ all of which have been 
found by various workers on tulips, are in reality 
but one and the same fungus. 

The Violet {Viola Odorata) 

Cultural Considerations, With violets the form 
of the house is not of great importance. In general, 
however, houses devoted to violets should be con- 
structed on the even span model. A three-quarter 
span house furnishes too strong a sunlight. 

Violets require an abundance of fresh air. Solid 
beds are preferred to the raised ones. In a house 
twenty-two feet wide there should be three walks, 
two and one-half feet wide. Each of the two outer 
beds should be one foot and nine inches in width, 
while each of the two inner beds should be seven 
feet wide. 

The temperature at night should never be raised 
higher than 45 degrees F. for the double flowered 
varieties, and 45 to 50 degrees F. for the single flow- 
ered varieties. The day temperature should never 
run higher than 60 to 65 degrees F. Violets thrive 
very poorly under high temperatures. If the mer- 



352 Diseases of Greenhouse Crops 



cury rises above 65 degrees, ventilation should be re- 
sorted to in order to lower the temperature. High 
temperatures force the plants to foliage with a de- 
terioration in blossoms. Violets thrive in a soil 
that is moist but well drained. The soil should be 
watered enough to keep it moist at all times, but it 
should never remain saturated for any length of 
time. Violets should be given all the ventilation 
possible every time the weather permits it. 

Diseases of the Violet 

Violets under glass are subject to numerous dis- 
eases. Success with this crop requires that these 
troubles be kept in check to a minimum. 

Cladochytrium Root Rot 

Caused by Cladochytrium viol^z Berl. 

This trouble is found in Europe, where it was 
first described by Berlese.* It has not yet been re- 
ported in the United States. This disease is mani- 
fested as swellings on the roots. The parasite is 
intercellular with branched mycelial threads. The 
globose zoosporangium terminates with an open tube 
through which the zoospores escape. Resting or sex- 
ual spores have not been recorded for this species. It 
is not likely that it will become an active parasite 
of forced violets. 

* Berlese, A. N., Riv. Patol. Veg. 7; 167-172, 1901. 



Violet Diseases 



353 



Downy Mildew 

Caused by Peronospora viol<z De By. 

Downy mildew produces indefinite spots on the 
leaves. In general appearance this trouble resem- 
bles that of the grape. The downy pale violet growth 
on the spot consists of a layer of the conidiophores. 
These are short, many times branched with small ul- 
timate branchlets. The conidia are short and ellip- 
tic. 

Smut 

Caused by Urocystis violcz (Sow.) F. de W. 

Symptoms, The disease produces prominent ir- 
regular swellings or blisters on root stalks, stems, 
petioles, and leaves. Soon the swellings rupture, 
exposing black-brown masses, and giving the affected 
plant a smutty appearance. 

The Organism. The spore balls are reddish brown 
and oblong to partly spherical. The sterile cells 
are yellowish with age, but the fertile cells are red- 
dish to light brown. The chlamydospores appear in 
balls of 4 to 8 spores. 

Control, Smut is usually brought in with in- 
fected cuttings or plants from out-of-doors. These, 
therefore, should be avoided. Infected plants should 
be destroyed by fire. 

Rust 

Caused by Puccinza viola (Schum) D. C. 
Symptoms, The rust is characterized by circular 



354 Diseases of Greenhouse Crops 



patches, the presence of which greatly distorts the 
attacked parts. All the three stages of the causal 
organism, secia, uredinia, and the telia are present 
on the same fungus. 

The Organism, The seciospores are orange yellow, 
subglobose, and finely warty. The uredospores are 
roundish and brown, possessing tiny warts. The 
teleutospores are black, elliptic to oblong, with 
thickened tip, and with a very slight constriction. 

Control. Violet rust is most prevalent on out- 
of-door plants, especially on the wild varieties. The 
disease is not of economic importance on indoor vio- 
lets. 

Crown Rot 

Caused by Sclerotinia lihertiana Fcl. 

This disease causes a rot of the crown as well as 
of the runners. This trouble is common in the cut- 
ting bed in which case it produces a damping off. 
In either case, the affected parts become soft and 
slimy. The disease is found only in leaky houses, 
or in beds with leaky water pipes. Attention to 
these points will check the trouble. For further 
description of the causal organism, see lettuce, p. 151. 

Thielavia Root Rot 

Caused by Thielavia basic ola (B. and Br.) Zopf. 

Thielavia root rot is perhaps one of the most im- 
portant troubles of greenhouse violet. The disease 
also attacks sweet peas, cyclamens, and asters. 



Violet Diseases 



355 



Symptoms, Diseased plants are dwarfed, with 
crinkled foliage, of a sickly yellow color. A closer 
examination will show that the seat of the trouble 
is confined to the underground stems and roots. In 
damp soils the former are often cracked, distorted, 
or covered with water-soaked spots. On the roots 
occur numerous brown or black lesions which eventu- 
ally girdle them. This girdling may take place at 
several points. Often the roots rot off (fig. 73, a), 
and all that remains is merely a short stub. The 
runners like the roots are often spotted or girdled 
in many places. The lesions first appear as a brown 
water-soaked spot which enlarges, the center becom- 
ing whitish and the margin black. On the leaf 
petioles lesions are often produced which are simi- 
lar to those formed on the runners. 

The Organism, Thielavia hasicola has several 
spore stages. The chlamydospores are composed of 
from four to eight segments (fig. 73, e and f.). 
The basal segments are usually empty. The others 
above are dark brown, with thick walls and are able 
to break up into individual cells each of which is 
capable of germination. Another spore type is the 
spore generating tube from within which are pushed 
out small cylindrical bodies with thin walls, that are 
known as endoconidia (fig. 73, c and d.). The 
latter too are capable of germination. The third 
spore form is the ascospores. These are borne in 
sacks within a main globose fruiting body known 
as the perithecium. The latter stage, however, is 
seldom found on diseased violets. The fungus is 



356 Diseases of Greenhouse Crops 



generally carried from year to year as chlamydo- 
spores in remnants of infected tissue in the soil or in 
the compost pile. 

Control, The fact that the harboring of chlamy- 
dospores in the compost is one of the means by which 
the causal organism is brought into the greenhouse 
at once suggests soil sterilization as a means of con- 
trol. This disease is often carried unconsciously 
with affected cuttings. From there the sand used 
for rooting the cuttings becomes infected. If the 
same sand should be used over again it will infect 
all cuttings planted there. Where there are no fa- 
cilities for soil sterilization the grower should make 
it a practice to use virgin sand every year. How- 
ever, a safer method is to disinfect the soil with 
formaldehyde. Reddick recommends the use of 
1 pint of commercial formaldehyde (40 per cent 
pure) to 125^ gallons of water. This solution is 
then used at the rate of 1 gallon to each square foot 
of bed space. Lime should not be used for violet 
beds, because lime favors the development of Thie- 
lavia. Careful attention should also be given to the 
watering of the plants. An excess of moisture in the 
soil favors the disease. It is doubtful that spraying 
will have any effect in controlling this trouble. 

Anthracnose 

Caused by Glceosporium viol(Z B. and Br. 

This disease attacks the edges of the leaves, start- 

♦Reddick, D. Trans. Mass. Hort. Soc: 85-102, 191 3. 



Violet Diseases 



357 



ing as an irregular discoloration which extends in- 
wards. Affected foliage rots and becomes unsightly. 
The acervuli are thin and few in numbers; the co- 
nidia are yellowish. 

Phyllosticta Leaf Spot 

Caused by 'Phyllosticta violcz Desm. 

Symptoms. This disease is characterized by nu- 
merous circular whitish spots, averaging about an 
eighth of an inch in diameter. Often the spots run 
together and involve the entire leaf (fig. 74, a.). 
The pycnidia are found on the dead tissue of the 
spots. The disease is commonly found on out-of- 
doors violets, but it is also met with under green- 
house conditions. The same disease also attacks the 
pansy. 

Organism, The pycnidia of the fungus are 
brown, minute, and numerous. The spores are mi- 
nute and subcylindrical. 

Control, It is probable that spraying with a stan- 
dard fungicide will control the disease. All infect- 
ed material should be destroyed by fire. 

AscocHYTA Leaf Spot, 

Caused by Ascochyta violcz Sacc. 

This disease is characterized by scorched appear- 
ing patches on the leaves. The affected plants soon 
become unsightly while the blossoms produced are 
stunted and valueless commercially. Little is known 



358 Diseases of Greenhouse Crops 



of the causal organism. Destruction by fire of dis- 
eased plants and diseased material is recommended. 

Speck Anthracnose 

Caused by Marsonia viol^ (Pass.) Sacc. 

Symptoms. The presence of the disease is marked 
by numerous small raised, black or brown colored 
spots on the upper surface of the leaf (fig. 74, c). 
The disease, so far as is known, is confined to the 
leaves, and has not yet proved to be very serious. 
Jones and Giddings * believe that the disease was 
probably introduced from Europe with imported 
cuttings. 

The Organism, Within the minute spots may be 
found the acervuli in which the spores are borne 
(fig. 74, b.). The spores are curved and one or 
two celled. The spetum is generally nearer one of 
the tips than in the center. 

Control, The disease may be kept in check by 
spraying with a standard fungicide. 

White Mold 

Caused by Zygodesmus alhidus Ell. and Halst. 

This trouble is generally manifested as a white 
flourlike coat over the leaves. Little is known of 
the causal organism, nor has it proven so far of any 
serious consequence. 

* Jones, L. R., and Giddings, N. J., Vermont Agr. Expt. Sta., 
Nineteenth Ann. Rept.: 234-235, 1906. 



Violet Diseases 



359 



Spot Disease 

Caused by Alternaria viol(Z Gal. and Dors. 

Spot disease is often known under the names of 
leaf spot, blight, smallpox, and rust. The disease 
constitutes a serious drawback to indoor violet cul- 
ture. In 1900, the violet industry of Alexandria, 
Va., had been practically abandoned because of leaf 
spot. From five to eight years before the appear- 
ance of the trouble the glass area devoted to violet 
in that vicinity was estimated at from 50,000 to 
75,000 square feet of glass. The term "violet dis- 
ease" is the one generally applied by the average 
grower. 

Symptoms. The disease attacks violets in prac- 
tically every stage of their development. Even cut- 
tings in the propagating bed are not immune from it. 
Generally plants which make rapid growth, but 
which are soft and succulent, are most subject to 
leaf spot. On the leaves the spots are at first small, 
but definite, usually circular, greenish, or whitish 
resembling the sting of some insect. The spots soon 
enlarge and the light central portion becomes sur- 
rounded by a narrow ring of discolored tissue, which 
is black or brown at first, but which fades as the spots 
become older (fig. 75, a.). Young spots are water 
soaked and semitransparent. In a few days, how- 
ever, the spots become dry, bleached, yellowish gray 
to white or pure white. Occasionally young spots 
fail to develop, dry and fall out, leaving a shot-hole 
appearance. Usually there are several spots on a 



360 Diseases of Greenhouse Crops 



leaf. These upon enlarging meet and coalesce, giv- 
ing the appearance of large, white blotches. The 
spores of the causal fungus develop on the spot un- 
der moist conditions only. 

The Organism. The fungus grows well on agar 
media, usually in concentric rings. The color of 
the mycelium is at first grayish white, but as the 
spores are formed the entire growth takes on an 
olivaceous tint due to the color of the spores. The 
conidiophores of the fungus are borne in clusters and 
are erect, pale olivaceous, and septate. The conidia 
are borne in chains on the tips of the conidiophores, 
and are flask shaped, muriform, and olivaceous (fig. 
75, b and c). 

ControL To control this disease it is necessary to 
have a clear idea of the factors which favor leaf 
spot under greenhouse conditions. Dorsett * enu- 
merates the following : 

"1. Not keeping the houses or frames clean, fresh, 
and sweet by frequently repairing and painting them, 
and by removing and destroying rubbish of all kinds 
as soon as it appears. 

"2. Not keeping the plants clean and in the best 
possible growing condition at all times. 

"3. Not selecting stock from strong, vigorous 
plants that have been entirely free from disease. 

"4. Not being careful to select only strong, vigor- 
ous, healthy stock from the cutting bed for planting 
in the spring. 

* Dorsett, P. H., U. S. Dept. of Agr. Div. Veg. Phys. and Path., 
Bui. 23: 7-16, 1900. 



Violet Diseases 



361 



"5. Not giving the proper attention to the selec- 
tion and preparation of the soil, to date and method 
of planting, and to care and cultivation of the plants 
during the growing season. 

"6. Not giving due consideration to the several 
varieties and their adaptability to the soil and lo- 
cation in which they are grown." 

It is evident therefore that these are important 
points to which the grower must give careful atten- 
tion. In addition and as far as possible preference 
should be given to those varieties which are resistant 
to leaf spot. Marie Louise, for instance, is a very 
susceptible variety. On the other hand, Lady Hume 
Campbell is said to be resistant. 

Since the spores of the causal organism may be 
introduced with the soil, steam sterilization is rec- 
ommended. Proper attention also should be given 
to the ventilation, watering, and heating of the 
houses. 

Cercospora Leaf Spot 

Caused by Cercospora viola Sacc. 

The trouble is characterized by large, dead, ashy 
spots on the leaves (fig. 74, d.). The centers of 
the spots are darker, due to the presence of the co- 
nidiophores. These are dark and short. The conidia 
are rod shaped, hyaline, long, slender, and many 
septate. 

Root Rot 

Caused by Fusarium violet Wolf. 

Symptoms, This disease is characterized by a 



362 Diseases of Greenhouse Crops 



sudden dying of the plants. Upon pulling it up we 
will find slightly sunken areas on the stem just above 
ground. The root system is generally destroyed, 
with the exception of a small stub. 

The Organis??!. Fusarium violcz was first de- 
scribed by Wolf."^ The sporodochia of the fungus 
are borne within the stems. The macrospores are 
hyaline, cycle shaped, 3-5 septate. The microco- 
nidia are small, continuous; condiophores short. 

Control. The disease is likely to occur where 
fresh barnyard manure is incorporated in the soil 
before planting. Care should therefore be taken to 
use only well rotted manure. Infected soils should 
be steam sterilized, or disinfected with formalde- 
hyde (see pp. 32-43). 

Wallflower {Cheiranthus cheiri) 

Cultural Considerations, Wall flowers require a 
cool house, with a night temperature not higher than 
45 to 50 degrees F. They thrive best when sup- 
plied with an abundance of water and ventilation. 

Fungi recorded on the wallflower. The wallflower 
is considered a very hardy flower, and is easily forced. 
The following fungi recorded on this host may 
prove serious : 

Cercospora cheiranthi Sacc, Peronospora para- 
sitica (Pers.) De. By. 

♦Wolf, F. A., Mycologia 11: 19-22, 1910. 



PART V 
GREENHOUSE PESTS 




showing web formation. 



CHAPTER 28 



plant pests 

Arachnides 
Red Spider » Tetranchyus himaculatus Harw. 

Red spiders or spinning mites (fig. 76, b) are 
very troublesome to greenhouse crops ; cucumbers are 
especially attacked by them. Eggplants and toma- 
toes are next in preference. Of the flowering plants, 
roses, violets, sweet peas, carnations, and chrysan- 
themums are also favorite hosts. The plants in the 
vicinity of greenhouses which are subject to the at- 
tacks of red spiders are beans, eggplants, celery, to- 
matoes, strawberries, clover, grasses, and weeds. 

Nature of Injury, The red spiders (fig. 76, a) 
feed on the under side of the leaves by puncturing 
and extracting the chlorophyll and plant juices in 
the cells of the punctured area. This soon results 
in small dead areas which become apparent as small 
whitish specks on the upper part of the leaf. In 
advanced stages, affected foliage become pale, whit- 
ish, transparent, and covered with minute dead pitted 
specks usually arranged in clusters. 

Control. Red spiders are at their best in hot, dry 
houses. They may be readily controlled by syring- 
ing with water. A strong but fine water spray de- 

365 



366 Diseases of Greenhouse Crops 



stroys their web and drives them off since red spiders 
cannot thrive under moist conditions. Plants with 
hardy foliage may successfully be rid of the spider 
by spraying with a solution composed of one-half 
pint of "Nicofume" liquid, and two quarts of con- 
centrated lime sulphur in 25 gallons of water. One- 
half ounce of salt dissolved in one gallon of water 
seems to control red spider on carnations. This, 
however, may burn the foliage of most other plants. 

Investigations by Vinal ^ seem to show that no 
fumigant was efficient in killing red spiders without 
severely hurting cucumber plants. Sulphur burned 
to form sulphur dioxide proved very effective in 
killing all stages of mites. However, since this 
gas is very deadly to plant life, it can only be used 
as a fumigant to free empty houses from spider in- 
festation. For the control of all stages above the 
egg stage, spraying with lemon oil or linseed oil 
emulsion proved very effective. Lemon oil may be 
used at the rate of 1 part in 20 parts of water, and 
applied thoroughly. For directions to prepare lin- 
seed oil emulsion, see p. 399. 

Mites (Tarsonemus palUdus Banks) 

Mites (fig. 78, a and b) are really closely related 
to red spiders. The species Tarsonemus palUdus is 
of particular interest to greenhouse growers because 
it attacks cyclamens, snapdragons, geraniums, and 
chrysanthemums. 

•Vinal, S. C, Mass/ (Amherst) Agr. Expt. Sta., Bui. 179: 153- 
182, 19x7. 




Fig. 77. 

a. Mite injury of geranium, h. of cyclamen. 



Plant Pests 367 



Nature of Injury. On the cyclamen (fig. 77, b), 
the work of the mites produces a gall. Usually both 
leaf and flower buds are badly affected. Infested 
plants are stunted, the foliage distorted, and the 
blossoms discolored. Instead of the normal soft 
pink or red, the petals become blotched and 
streaked; ultimately the flower wilts and dies pre- 
maturely. On the geranium (fig. 77, a, and fig. 79, 
b) the attack by the mite causes the foliage to curl 
and to drop prematurely. Often, too, the injury 
becomes noticeable as scorched spots on the leaves. 
Injury is most severe when the plants are crowded, 
the leaves touching each other, and the humidity 
high. In this respect, therefore, the mite differs 
from the red spider, in that the latter only thrives 
under droughty conditions. On the snapdragons 
(fig. 78, a and b, fig. 79, a) and chrysanthemums 
the attacked foliage becomes curled and distorted, 
and the flower buds, too, swell somewhat, and be- 
come distorted and useless. The same pest also at- 
tacks the blackberry out of doors (%. 79, c). 

Control. At first, mites seem to attack the cycla- 
men during dry weather. Later, however, poor cul- 
tivation, poor ventilation, and excessive moisture in 
the house seem to encourage the work of the pest. 

With geraniums some varieties seem to be more 
resistant than others. Garman states that the va- 
rieties Le Pilote, Jean Vroud, S. A. Nutt, Alphonse 
Ricard, Madam.e Kowalevski, Baron Grubissich, 

♦Garman, P., Maryland Agr. Expt. Sta., Bui. 208: 327-342, 
1917. 



368 Diseases of Greenhouse Crops 



Maryland, Beaute Poitevine, Mme. Laudry are all 
susceptible to the attacks of the mites. On the other 
hand, the variety Le Favorite seems to be immune. 
It is not known whether or not there arc resistant 
varieties of cyclamen, chrysanthemum, or snapdra- 
gon. Because of the extremely primitive respiratory 
system of mites, it is difficult to keep them in check 
by fumigation with various gases. It is safer there- 
fore to resort to spraying. However, when a plant 
becomes badly infested, no attempt should be made 
to save it. It will be cheaper to destroy it by fire. 
Dusting with tobacco or sulphur will do little good. 
Moznette * obtained good results by dipping the 
plants in an oil emulsion called Yel-ros mixed in 
the ratio of one part of Yel-ros to forty parts of 
water. Yel-ros contains a good deal of Xylol which 
is penetrating. This treatment, however, is recom- 
mended for older plants. Young plants may be 
greatly injured by burning. "Black leaf 40" and 
water in the ratio of 1 to 1,000, or of one teaspoon- 
ful to a gallon of water will effectively control the 
mite. By adding three to four pounds of ordinary 
soap to each 100 gallons of the above solution, it 
will be made to adhere better to the treated plants. 
Spraying should begin before the mites attack the 
plants and should be continued every ten days until 
the flower buds are ready to open. At this stage the 
spraying should cease as otherwise the petals may be 
discolored. 

* Moznette, G. R, U. S. Dept. of Agr.. Jour. Agr. Research 
10:373-390, 1917. 




Fig. 78- 

c and b. Snapdragon mite injury, c and d. adult male and female mites. 



CHAPTER 29 



GREENHOUSE THRiPs {Heliotkrips hczmorrJioidalis 

Bou.). 

Greenhouse thrips often cause considerable 
damage to ornamentals, while their presence may not 
always be detected. The damage caused by thrips 
is confined to the foliage. The adult and the larvse 
of the thrips feed by puncturing and lacerating the 
epidermis and by sucking the plant juices. The in- 
jury at first becomes apparent on the older leaves, 
and later spreads to the younger ones. The trouble 
first appears on the under side of the leaves in the 
form of minute white epidermal spots. Later, as 
the spots become more numerous, they unite, form- 
ing large blotches. At this stage, the injury becomes 
apparent on the upper part of the leaves as a dis- 
tortion between the lateral veins, and by wilting 
and dying of the edges. Both sides of the infested 
foliage soon become covered with minute drops of 
a reddish fluid which finally changes to black. These 
drops are voided by the thrips. Affected foliage be- 
comes white and drops off prematurely. In the 
greenhouse, thrips may attack azalea, aspidium, cro- 
ton, dahlia, phlox, verbena, pink, ferns, palms, ficus, 
and fuchias. 

Control. The easiest way to keep this pest iu 

369 



370 Diseases of Greenhouse Crops 

check is in burning nicotine papers at the rate of 2 
sheets to every 1,000 cubic feet of greenhouse space. 
Fumigation is best performed at night in a moist 
atmosphere. Early in the morning the treated house 
is opened and thoroughly aired. Fumigation with 
nicotine liquid extracts is also effective in controlling 
thrips. Russell * recommends the use of one ounce 
of liquid nicotine (containing 40 per cent, nicotine) 
to every 1,000 cubic feet of greenhouse space, or 
from one and a half to two ounces of the weaker 
strengths. The liquid is evaporated over small 
lamps or stoves, and to prevent scorching is diluted 
with water. Greenhouse thrips may also be kept in 
check by fumigation with hydrocyanic-acid gas. 
For directions, see p. 385. 

Mealy Bugs {Pseudococcus sp.J^ 

Mealy bugs are really scales without armor. They 
are sprinkled over with a white mealy wax or pow- 
der which gives them the name. In the greenhouse 
there seems to be but two species of importance, 
namely, Pseudococcus citri and P. longispinus. 

Control. The easiest way to keep this pest in 
check is to liberally syringe the plants with water 
at a fair pressure. This will wash the insects off the 
plants and permanently dislodge them. Spraying 
with a mixture of one paft nicotine sulphate to 750 
parts of water will also keep them in check. Fumi- 

* Russell, H. M., U. S. Dept. of Agr., Bureau Entomology Cifd 
151:1-9,1912. 




Fig. 79. 

a. and h. Snapdragon and geranium injury 
(after Garner), c. mite injury of blackberry. 



Fig. 8o. 

a. Mustard plant badly infected with the green aphid, 
b and d. parasitized aphids, the circular holes on the 
backs are openings through which the adult Aphidius 
testaceipes emerged, c. lady beetle. 



Greenhouse Insects 371 



gation with five ounces of cyanide to each i,ooo 
cubic feet of space for one hour will also be effective. 

Scale Insects 

There are various scale insects which attack green- 
house plants. The black scale, Lecanium ole(Z^ at- 
tacks the geranium and roses. Lecanium tessellatum 
attacks palms. Aspidiatus nerii attacks a large and 
varied number of house plants. 

Control. The safest method of treatment is fumi- 
gation with hydrocyanic-acid gas. For directions, 
see p. 385. 

White Fly {^Alleyrodes vaporaiorum West) 

The white fly is considered one of the worst 
pests of some greenhouse crops. The plants most 
affected are cucumber, lettuce, tomatoes, eggplants, 
chrysanthemums, coleus, geraniums, and roses. The 
pest injures the plants by attacking the underside of 
the leaves and by sucking the tissue juices. The 
insect deposits a sweetish, sticky substance which 
tends to clog the stomata of the leaves, and frequent- 
ly serves as the host for a sooty mold. 

Control, White flies may be controlled by fumi- 
gating with hydrocyanic-acid gas. For directions, 
see p. 385. 

Plant Lice or Aphids {Aphididcz) 

Plant lice (fig. 80, a) derive their food by suck- 
ing the plant juice. In the greenhouse there seem 



37^ Diseases of Greenhouse Crops 



to be four important aphids which attack plants^ 
The melon aphis {Aphis gossypii) is a general 
feeder and attacks a large number of plants. The 
green aphis {N ectorophora rosd^) seems to attack the 
rose only. The brown aphis {Rhopalosiphum violcz) 
attacks the violets. The black aphis {N ectorophora 
chrysanthemicoleus) attacks the chrysanthemum. 
The following table by Davis * is a list of plant 
lice which are known to attack ornamentals in the 
greenhouse : 

•Davis, G. C, Michigan Agr. Expt. Sta., Special Bui. 2: 5-43, 
^896. 



Greenhouse Insects 



373 



Table i8 
List of Aphids Attacking Ornamentals 



H 0) 

I § 

S o 



a 



O CI 

be ui 



S '='2 2 

£ 8 a a 

® w A « S 

•s^-s a a 
a-1^23 

•a l^-^-i 

^'-^ ^ 

MM t; 03 c3 a.S 



ei-5 

(D O 

^a 

o o 

as 



a « fl fl 

<U .(DO) 

a^sa 

« o o o « 



11 



^ a 



O M 



a| 



03 

^" 0 .2 




D-d 



OH-- d M .'^'^ fl d g o ^ fl.ii . 

- - " -J gt>.^ ««aa§5«^'^a'='^ 

i^j3 ft ft,a ftftaJ <uj3,£4^ ft^^ft ^ ^ 



|ao 



"ft2 



ilgilllill 

ft'^ S5-a'5o c3 cs 2 c'a 

llg&'isagoo 

o as o ft.2.2.s.2 m 
.S-^ o.&^S aftftftft 



ft' 3 

""si 

So 



OS 03 

a& 
« 



0.2'^ 

s « s a ^5 ft.^s-2i5 a « 

•I § I •^S.3|-S.2.2g| 



bo ft 



q-a 

o o 



374 Diseases of Greenhouse 

Table l8 (continued) 



Crops 




Greenhouse Insects 375 



Control, Aphids may be controlled in the same 
way as thrips (see p. 369). They are also kept in 
check in nature by lady beetles (fig. 80, c) which 
feed on them, and by a fly, Aphidius testaceipes 
(fig. 80, b and d). The adult female of this fly lays 
its eggs in the body of the aphis. The eggs upon 
hatching give birth to a small legless larva which 
feeds upon the interior vital parts of the plant louse. 
When the larva is fully developed it pupates and 
cuts a circular hole on the top of the body, emerging 
as a winged insect ready to attack other aphids. 

Soil-Infesting Insects 

Soils infested with insect pests are as sick as when 
infested with eelworm or parasitic fungi. The green- 
house man in sowing his seed has often great diffi- 
culty in obtaining a good and even stand. Fre- 
quently the stand is reduced by fifty per cent, in 
spite of the many resowings. The cause of this may 
be traced to the presence in the soil of certain in- 
sect pests. Among those dreaded most are: Cut- 
worms (Agrotis sp.), (Lycophotia sp.), (Peridroma 
sp.); wireworms (Melanotus sp.), and white grubs 
(Phyllophaga sp.). 

ControL Spraying the soil will be of little value 
in the control of underground insect pests. Fortu- 
nately, however, we have more effective means for 
dealing with them. To destroy wireworms, sow 
corn which has been soaked for ten days in water 
containing arsenic or strychnine sulphate before 



376 Diseases of Greenhouse Crops 



planting the regular crop. The larvae will feed on 
the poisonous com kernels and die. Another way is 
to treat the seed with gas (coal) tar. 

White grubs may be controlled by the use of bi- 
sulphide of carbon. 

Cutworms may be controlled by the use of a poi- 
soned bran made as follows : to three ounces of mo- 
lasses add one gallon of water and sufficient bran 
to make a fairly stiffened mixture. To this add 
Paris green or arsenic and stir well into a paste. A 
heaping teaspoonful of the mixture is scattered here 
and there over the infested beds. 

Ants 

Ants are often troublesome in the greenhouse. 
These may feed on germinating seed or on growing 
tips of tender plants. A more pernicious habit is the 
care and protection which they afford to plant lice 
and mealy bugs. 

Control. Ants may be controlled by being fed 
with a poisoned bait prepared as follows: To yj^ 
pints of water add one-fourth of an ounce of tartaric 
acid (crystals), 15 pounds of granulated sugar. Boil 
this mixture slowly for 30 minutes and allow it to 
cool. Then slowly dissolve three-fourths of an 
ounce of sodium arsenate in one-half pint of hot 
water and allow it to cool. After this is well stirred 
into the sirup above mentioned, add one and a half 
pounds of pure honey. This mixture may now be 
sprayed on paper or boards on the beds. The ants 



Greenhouse Insects 377 



being fond of sweet foods will be attracted, and 
upon feeding on it will be poisoned. 

Hot House Milliped {Oxidus gracilis) 

These "thousand legged'' little creatures are very 
common in beds in which have been mixed large 
quantities of rotted manure or leaf mold. They 
often attack sprouting seeds, either devouring or 
seriously injuring them. These millipeds may oc- 
casion considerable damage in cucumber beds. The 
common species is Oxidus gracilis. However, an- 
other injurious form often met with is Julus vir- 
gatus. 

Control, Gossard of the Ohio Experiment Sta- 
tion recommends the application of tobacco dust 
mulch to the infested bed. This is spread out evenly 
and worked in one-half to one inch deep. A mix- 
ture of nicotine sulphate and water in the proportion 
of 1 to 700 when applied to the infested soil will 
also help to destroy the millipeds in the beds. They 
may also be poisoned by placing at various intervals 
on the beds slices of pumpkin previously dipped with 
phosphorus rat paste. 

Sow Bugs, "Wood Lice,*' Isopods 

Sow bugs are abundant under potted plants or in 
damp secluded places. Besides feeding on dead ani- 
mal and vegetable matter, they also feed on living 

♦Gossard, H. A., Ohio Month. Bui. 3: 55-56, 1918. 



378 Diseases of Greenhouse Crops 



plants. They prefer orchids and similar plants be- 
cause they can hide in the moss and feed on the 
fibrous roots. Carnations also are often attacked by 
the same pest. 

Control. Tobacco dust and nicotine solutions are 
ineffective in controlling sow bugs. Sliced pumpkin 
treated with phosphorus rat paste is an effective 
remedy. 

Slugs 

Slugs or snails often cause considerable damage to 
greenhouse plants. These pests feed at night and 
usually hide during the day. They secrete a slimy 
mucus as they travel. By dusting the plants with 
ashes, lime, or any caustic dust, the latter will ad- 
here to the slime of the body, which upon drying soon 
exhausts the creatures in their struggle to be freed. 



PART VI 
METHODS OF CONTROL 



CHAPTER 30 



METHODS OF CONTROL 

From a practical consideration the greenhouse 
grower is directly concerned in finding control 
methods to keep the various plant diseases under 
check. Fortunately, there are numerous methods 
which if followed out intelligently may be the means 
of reducing losses to a minimum. These methods 
may be enumerated as follows : 

1. Soil sterilization. This method has been 
fully discussed under chapter 3, pp. 32-43. 

2. Seed treatment, taken up in chapter 8, p. 104. 

3. Spraying. 

4. Hygiene. 

3. Spraying 

While the orchardist has learned the necessity of 
spraying, it is doubtful whether greenhouse growers 
have sufficiently realized its value. Spraying has 
two aims : to kill the insect and animal pests, and to 
control fungous diseases. The substances which are 
used for the one purpose are without effect on the 
other. 

Insecticides 

All animal and insect pests are best controlled by 
the use of poisonous mixtures applied in the form 

381 



382 Diseases of Greenhouse Crops 



of liquid sprays or in powders. Insecticides may 
be classified as internal or stomach poisons, and ex- 
ternal or contact poisons. 

(a) Stomach Poisons. Paris green is one of 
the oldest stomach poisons. When chemically pure, 
it is composed of copper oxide, acetic acid, and 
arsenious acid. It destroys cutworms, caterpillars, 
beetles, grubs, slugs, etc. It should be applied pref- 
erably as a liquid, using one pound of the poison 
and two pounds of lime to two hundred gallons of 
water. The Paris green tends to sink to the bottom 
of this mixture, unless constantly stirred while be- 
ing applied. This chemical is often adulterated with 
white arsenic, causing it to scorch the treated plants 
badly. Therefore for greenhouse crops the use of 
arsenate of lead is to be preferred, since it is less 
liable to scorch the foliage, and also because it ad- 
heres better. Its chemical composition consists of 
acetate of lead and arsenate of soda. It is applied 
to the best advantage as a liquid, composed of about 
three pounds of powdered arsenate or five pounds of 
paste arsenate to one hundred gallons of water. 

Arsenite of zinc may also be used. It is a very 
finely divided fluffy white powder which can be thor- 
oughly distributed and which adheres well to the 
foliage. It is intermediate between Paris green and 
lead arsenate in strength, and costs less than either. 

7/ is essential when arsenicals are used to see that 
they are correctly labeled^ and kept under loch and 
key^ as they are poisonous to both man and animal. 

Hellebore or white hellebore is somewhat less dan- 



Methods of Control 383 



gerous than the arsenicals. However, it loses its 
insecticidal value by being exposed to the air. It 
is a specific against slugs. 

(b) Contact Poisons. These are used most 
extensively in the greenhouse. 

Water. Every florist appreciates this simple and 
effective remedy. To be effective in dislodging and 
destroying soft-bodied insects, it must be thrown 
with considerable force on all parts of the plants. 
For this purpose a good nozzle attachment is very 
necessary. This simple remedy is effective in de- 
stroying red spider, white flies, and mealy bugs. 

Tobacco, There are few substances which are 
more extensively used than the many commercially 
prepared tobacco products. Finely ground tobacco 
is extensively used as an insecticide, especially for 
Aphids. The product known as nicofumes is ex- 
tensively used for indoor fumigation. 

Tobacco Decoction. This may be prepared by 
boiling for one-half hour one pound of tobacco stems 
in two gallons of water. It is then strained and 
more water added to replace that which was lost by 
evaporation during boiling. The liquid is used as 
a spray against plant lice. 

''Black Leaf and ''Black Leaf 40:' These are 
two commercial products. The latter is the more 
concentrated of the two and is extensively used in 
the control of sucking insects. The following table 
by McCue shows the dilutions that should be 

*McCue, C. A., Del. Agr. Expt. Sta., Bui. 97: 17, 1912. 



384 Diseases of Greenhouse Crops 



used to give a nicotine content varying from 0.03 to 
0. 1 per cent. 

Table 19 





''Black Leaf" 


T Black Leaf 40" 


Nicotine Contents 










Parts 


Parts 


Parts 


Parts 




''Black Leaf" 


Water 


"Black Leaf 40" 


Water 


.03% 


I 


123 


I 


1600 


.04% 


I 


92 


I 


1200 


.05% 


I 


73 


I 


960 


.06% 


I 


61 


I 


800 


.07% 


I 


52 


I 


685 


.08% 
.09% 




45 


I 


600 


I 


40 


I 


532 


.10% 


I 


36 


I 


480 



Soap, Any good soap may effectively be used 
as a contact insecticide. The best soap is that which 
is made with caustic potash rather than with caustic 
soda. Soda soap washes are apt to gelatinize when 
cold and are made difficult or impossible to be used 
as a spray. Fir tree oil soap may be used at the 
rate of three ounces to each five gallons of water 
without injury to plants. Whale oil soap should be 
used at the rate of only one-fourth pound to each 
gallon of water. A stronger solution may injure 
tender plants. 

Sulphur. This is used not only as a fungicide, but 
also as an insecticide as well. When used as a fumi- 
gant, sulphur at the rate of one-third of a pound to 
each 1,000 cubic feet of greenhouse space will be 
effective. When ready to fumigate the house is 
closed tightly, the required amount of sulphur 
weighed out and divided into four equal parts on 



Methods of Control 385 



clean paper. The sulphur is then placed in wide, 
deep metal pans at the bottoms of which are first 
placed chips which have been soaked in kerosene. 
The pans are solidly placed at equal distances on 
raised bricks in the center aisle of the house. When 
all is in readiness fire is set to the chips. When 
these begin to burn well the sulphur is spread evenly 
on the burning chips of each pan. As soon as the 
sulphur ignites, the operator should run out and shut 
the door of the house as quickly as possible. Sulphur 
fumes have an irritating and suffocating effect on 
man. The sulphur fumes should be allowed to act 
for at least twelve hours before one opens the house. 
The sulphur fumigation may be started at any con- 
venient time during the day or night. This treat- 
ment will destroy red spider and mildew. 

Hydrocyanic-Acid Gas, There seems no doubt 
that fumigation with hydrocyanic gas offers the 
cheapest and most efficient method of controlling 
white flies, aphids, thrips, scales, and mealy bugs. 
However, this method has not yet gained general 
popularity because of the deadly nature of the gas 
and its injury to plants when overdone. The best 
generators for the gas are one-half or one gallon 
glazed earthenware jars. When ordering generators 
it should be indicated that tops are not desired. 

Before fumigating it is essential to see that all 
broken glass is repaired, and that all cracks are care- 
fully stopped up. It is very essential that the cubi- 
cal contents of the greenhouse be accurately deter- 
mined. To secure the cubical contents of an even 



386 Diseases of Greenhouse Crops 

span house compute the number of square feet in 
the rectangle and in the right angles, and multiply 
the sum of the three by the length of the house. 
To secure the cubical contents of a three-quarter 
span house multiply the sums of the areas of the 
rectangles, and the areas of the right angle triangles 
by the length of the house. In estimating the cubi- 
cal contents of a greenhouse it is not necessary to 
make allowances for the space occupied by pots or 
benches. Fumigation should never be attempted 
during high winds. It should never be done during 
the day and not earlier than one hour after sunset. It 
is never wise to fumigate when the outside weather is 
near the freezing point. Nor is it well to fumigate 
during humid nights. The best time to fumigate is 
when the temperature ranges from 55 to 68 degrees 
F. 

The chemicals required for fumigation are either 
sodium cyanid (NaCN) or potassium cyanid 
(KCN), sulphuric acid (H2SO4), and water (H2O). 
Sodium cyanid is preferred. It should be free from 
chlorin and contain not less than 51 per cent of 
cyanogen. Cyanid is a violent poison. It should 
be stored in airtight cans and carefully labelled 
''Violent Poison." Commercial sulphuric acid of 
66 degrees Baume or 1 .84 specific gravity will answer 
the purpose. Upon referring to Tables 20 and 21 
we see at a glance the amount of cyanid per each 
1,000 cubic feet necessary to kill the particular in- 
sect and the amount each plant can stand. For ex- 
ample, if one-half ounce of cyanid as indicated in 



Methods of Control 387 



Table 21 is used per 1,000 cubic feet of space, and if 
the greenhouse to be fumigated contains 1 5,000 cubic 
feet, then multiply the number of cubic feet con- 
tained in the greenhouse by the amount of cyanid 
to be used per 1,000 cubic feet, 1,500 times 
equals 7.5 ounces cyanid. If there is the least doubt 
as to the amount of gas the plant can stand without 
injury the initial dose should not exceed one-fourth 
ounce for each 1,000 cubic feet of house space. 

Table 20 



Amounts of Cyanid and Number of Fumigations 
Sufficient to Destroy Various Greenhouse Pests 





Ounces per 


Number of 


Interval] 


Insects 


1,000 Cubic 


Fumigations 


Between 




Feet 


Required 


Fumigations 








Days 




y2 


I 






HI 


I 




Thrips 




2 


10 






3 


7 to 9 


Long scale 




I 




**Greenhouse orthezia .... 




2 


21 to 28 






I 






2^ 


I 




**Long-tailed mealybug . . . 




2 


do. 




2y. 


2 


do. 






2 


do. 




2y2 


2 


do. 






2 


do. 




2y 


2 


do. 


Tessellated scale 


2>^ 


2 


do. 


Florida fern caterpillar .... 


5 


I 






5 


2 


do. 



*For the most part aphids can 'be controlled with one-half ounce 
of sodium cyanid per 1,000 cubic feet, although there are a few 
species which are quite resistant to this gas and not so readily killed. 

fThe greenhouse Orthezia and mealybugs around the roots of 
plants are very difficult to kill, and this dosage is recommended only 
for those occurring above the soil. 



388 



Diseases of Greenhouse Crops 



C3 U 



O « 



^ a o 



o o 



3^ 

V, S ^ S 3 

o66d"Sooooooooooooo+^3-" 
§ o " 0-2* 



. a .13 

o < 



. 6 « 

i <U i3 

c ft 



O 3 



3:2 

■S5 c 

Oh 



6:2 

3 c 
t/20 



. a 



■;3 -c 



3 

w 
O 

a ■ o to . 



<<< «« 



<«5<; <<«<« 



6 

£.2 



1-^ 



HO. 



Methods 



of Control 



81 



O "5 





1 








. . . . 

vp O O O O 
'O 'w 

o 


Ov 


o 

M 



§ O 

HZ 



1- c 



II 



6 6 6 d d-;^ 5 p d 6 ^3 d 6 d S)3 6^ £ 3 6 ddddd 
.SPo "TJo (DO St^o 



'o 



(D O 
ZZ 















• « 

















0) OS oJ . <u 

o « o 



•o 



JO o o o o 
Vj-j 13 13 »0 



, 6 » 

i b 

2^ S 2 

o a 

,G 



OS 



oO 
a, 



s:2 

Or ^ 



« > 

. . . . ni ..2 E3 

o o o o 



03 u> y) p 



a 

o 

2 1 > 



C G 
O nJ 

In do 

o 



390 



Diseases of Greenhouse Crops 



Si 



65^ 



C.3 

5 6 6 6 6—^ 
HZ 



COOCJj^COO 



6 6 d 6 6 d d 

"O "CO 't) "tJ "O 



• • 3 

••| 

. .2 

O O M 
V 

Z 



rt ■'^ •— J 
= S S = o 



k: ^ g 

R-S o 



CO 

si 



5 >> 



o « o • « 



in in t» o 



.5Ji o o o o d t; 
UUOOUUUU 



du 



:.2 :5:5 



d:= cj.^ ^ " 



■ o:i5 



•2 w 



6i 



e : 

"S : 



S ^ S 



S o >. 



-S^^ X -^-i; i:5 ^- 3 3 3 S 



rt O 



Methods of Control 



o 



goo 



O O O -u M 

tj'd'd " bo 



o c 

u u 

o o ^'^ 
-rJ'O ^Xi 
<u o 



w s 



5:2 

PL, 



Or ^ 



N N N N li 



a-s 8-a t'Bv.s.B 

O ft'O Jjrd '^7^ o 

b ^-^ 

C V-' O O. 



aaaaii2a" & . 

3 :J 3 s S.3"a'a ni7=5 o 

.wrt-rt.rt Oi Qj »-i t-i tn Pi 



o o o 
* * * 



da 



o^ 



i/i in 

'o'o 

ft ft 

(U Q> 



3 o '"•Sh -i 



o -rt 



.S3 i 



m ft 

1-1 JJ 3 

'O -£3 -M 2 2 



392 Diseases of Greenhouse Crops 



O ^ 



vO C3 TO 2 



lag. 



a 

O 



• • tt) • 

: : o : 

.& o .5f o 



g 6? 



&'^^-^-§-S^S-^'^'^'0'S^^2'^ 

oj o o o .2f o.S- o o 



ID 

• ^ 

■»-> 

a 
o 



3 
o 

p. ^ 



m O 



aj 03 
o a 



0) 



O 3 

"in o 

IS 



is 



6:2 

^ >> 



'3 S o 



S c 



S5 



° g^: o S c g c c - 



to to 



as 



Methods of 



Control 



SI 



O n! 



;3 m'^ 

O lOOO o o 
O C505 '-to 



6X! s 

HZ 







to 






do. ; 


a 
•J 




%0 


M 

o 




o 











II . 

o o o o o o 3 o o o o— o o 



•S-o 
HZ 



fl.S .S 
d 6 6-° S 6 3 d 

.&0 O 

HZ Z 



t3 o) 

<50 



73 

1-1 



^1 DC r-j 

o t« o-" o 



o on 



4( <U I-" 

<uH ^ 

« (U C(J 

o o< 



O =s 



oO 
a, 



6:^ 





: :^ : 


.' Iio • • • 





^2 S g 



o ..^ o Pi 

3 i3 



■i 

' u 

2 :i 
o . s 
- s •§ 

a ^ o 

Jh S « 

• • -S 

O £3 O C.5 3 



a a 
szzz 



Diseases of Greenhouse 



Crops 



O tn 



O "5 



^1 

li. 



o -e 3 o o o 



a, g 



on 

C3 DQ 



d66-*2S2o fcigoodd dodo 



73 T! -a 



gH5 



^ 4> 



a 0) 
O d 

-2 q 



oO 
0. 



6:2 



(N U5 



8 d ^ « 



c3 cS 

4) a> 



uo' 



£ 3 " 
3 03 O 

axi a 
6 6 TO cs ^ 



o g S o o 



• a 2 

O o3 R 

asai 
.2.S.S:g 

a a a-g* 

aaa>^ 
>> >> >,o 



Methods of Control 



o o o o o 



E3>.-.5at3.... 

oooooooooooo2oooo*fc.goooo 

o Q"^ o 

H ^ 



u S? 
o o, 



3 



O ;3 



Is 

cO 



3 G- 



a^agi : :i 
a 

S oj c 

aaiaaaa 

O O (- o o 

t-i i^'^ t-i u 

fl a <u c a a.; 



•-^a-Sia 



,a ^ 



H •-. S a 



<a « ^ 4' a cc 00 a3.pTi,.S ..2 

alia-aaaaa-^g-^&l : .gs 



as 



fed) -PS 2 

^-£3 J3 B S 



396 Diseases of Greenhouse Crops; 



fin 



O O Xi 

m| d 6 6 2 

WO S 



j3 



i J 



CO « 

O 3 



1:^ 



S:2 

3 c 



it 

^ o 



•B . a 

2 --C 



Methods of Control 397 



Mixing the Chemicals. The chemicals should be 
mixed as follows : For each ounce of sodium cyanid 
use i}4 fluid ounces of sulphuric acid and 2 fluid 
ounces of water. The water is first placed in the 
generators, then the sulphuric acid. The cyanid is 
then dropped into the warm acid, and the manipula- 
tor must at once leave the greenhouse and shut the 
door tightly behind him. 

Short exposure with a greater strength of gas is 
more desirable than overnight exposure with a 
weaker gas. Better results are obtained when the 
fumigation lasts about two hours. After fumigation 
the house is opened at the top or at the side doors 
to allow the escape of the gas. During cold weather 
the ventilators should be opened for a short time 
only at several intervals. 

It is not advisable to fumigate if the house tem- 
perature is below 52 degrees F. or above 70 degrees 
F. As already stated, fumigation should never be 
done while the sun shines. Hydrocyanic acid gas 
is soluble in water. It is, therefore, evident that 
neither the plants nor the benches should be wetted 
before fumigation. 

Don'ts in Fumigation 

The following don'ts laid down by Sasscer and 
Borden will be of value to the greenhouse man : 

"Do not guess the amount of chemicals to be em- 
ployed or the cubic contents of the house. 



398 Diseases of Greenhouse Crops 



"Do not fumigate plants in a greenhouse in day- 
light. 

"Do not fumigate when the temperature in the 
greenhouse is below 52 degrees or above 70 degrees F. 

"Do not leave the chemicals within reach of those 
unacquainted with their poisonous nature. Always 
have them properly labeled. 

"Do not handle the chemicals any more than is 
absolutely necessar5^ It is well to have a pair of 
old gloves for this, and to use them for no other 
purpose. Always wash the hands thoroughly after 
handling the chemicals whether gloves have been 
used or not. 

"Do not allow the acid to splash or drop on the 
clothing or skin. 

"Do not stay in the greenhouse any longer than is 
necessary to place the cyanid in the jars, and never 
enter a greenhouse charged with the gas until it has 
been thoroughly aired. 

"Do not fail to post danger signs at all entrances 
before setting off the charge, and to see that the 
greenhouse is closed tightly. 

"Do not attempt to fumigate a large greenhouse 
alone. 

"Do not fumigate a greenhouse adjoining a dwell- 
ing without notifying the occupants before fumi- 
gation. 

"Do not pour water on the acid; pour acid on the 
water. 

"Do not become negligent in any of the precau- 
tions; to do so may cause serious results." 



Methods of Control 399 



Emulsions 



Kerosene Emulsion, The formula for kerosene 
emulsion is as follows: 



Dissolve the soap in the water by heating. Re- 
move the soapy water from the fire and add the kero- 
sene and the liquid, violently mixing until a stable 
milky emulsion is formed. This emulsion should 
afterwards be mixed with water without the kero- 
sene separating from it. As a spray for soft-bodied 
sucking insects, the above stock solution should be 
diluted ten to twenty times. Kerosene emulsion is 
not extensively used in greenhouses. 

Linseed Oil Emulsion, Linseed oil emulsion has 
been recommended by Vinal"^ for red spider on green- 
house cucumbers. The emulsion according to Vinal 
is made as follows: 

(a) The necessary articles for preparation are: 

1. Bucket pump. 

2. Container or mixing tank. This should hold 
at least eight or nine gallons. For this purpose a 
small washtub is perhaps the most available. Pails 
may be used, provided the materials are mixed pro- 
portionally. 

3. Ivory soap. 

4. Raw linseed oil. 

5. Hot water. 

♦Vinal, 8. C, Mass. Agr. Expt. Sta., Bui. 179: 175-176, 1917. 



Kerosene . 

Water 

Hard soap 



2 gallons 
I gallon 
^ pound 



400 Diseases of Greenhouse Crops 



(b) The following proportions of materials for 
TOO gallons of spray are used: 

1. Five gallons of hot water. 

2. One and one-half pounds of Ivory soap. 
(Six 5-cent cakes or three lo-cent cakes.) 

3. One gallon of raw linseed oil. 

(c) Steps in the preparation of stock solution 
follow: 

1. Put the required amount of hot water in the 
container. 

2. Shave the Ivory soap into this and stir until 
completely dissolved. 

3. If at this time the temperature of the soap so- 
lution is too hot for the hand to bear, dilute with 
one gallon of cold water and let it stand until about 
body temperature or lukewarm. The cooling of this 
solution is necessary in order to prepare a permanent 
emulsion ; otherwise the oil will come to the surface 
on standing (see No. 6). It also prevents the chemi- 
cal and physical killing properties of the linseed oil 
from being changed by heat. 

4. Add slowly, while stirring vigorously, one gal- 
Ion of linseed oil. 

5. Completely emulsify by using the bucket 
pump and turning the stream back into the container 
again, keeping the nozzle below the surface of 
liquid. Five minutes' vigorous pumping should 
completely emulsify this solution. 

6. Set aside for a few minutes while preparing 
spray tank in order to see that oil does not come 
to the surface. 



Methods of Control 401 



(d) The following are directions for the prepU' 
ration of spray tanks and spray: 

1. Fill the 100-gallon spray tank about one-half 
full of water. If the water used is too cold, upon 
the addition of the stock solution the soap will 
solidify into small lumps, thus spoiling the emulsion. 
This may occur early in the spring, when the water 
is very cold, but later in the season ordinary top 
water may be used without danger of the soap solidi- 
fying on the addition of the stock solution. 

2. Add stock solution made above. (See (c) 
1, 2, 3, 4, 5, 6.) ^ 

3. Agitate. (If lumping occurs, the addition 
of a few pails of hot water will remedy this.) 

4. Fill the 100-gallon spray tank. 

Fungicides 

These poisons are used to control fungous diseases. 
As previously stated, some parasitic fungi live on 
the surface of the leaves and stems and are therefore 
easily controlled. An example of this is the powdery 
mildew. Other fungi, and these are in the larger 
majority, are those which live parasitically within 
the tissue of the host, and therefore cannot be reached 
by any spray. Fungicides are helpful only in pre- 
venting entrance of the parasite in the host. They 
are as ineffective in controlling insect pests as are 
insecticides in controlling fungous diseases. 

The author has often referred in this work to the 
term "standard fungicide." In reality there is no 



402 Diseases of Greenhouse Crops 



one standard fungicide. The term as employed here, 
however, refers to any effective fungicide that is 
best adapted to each particular case. For instance, 
Bordeaux mixture may be termed "standard" if used 
to spray greenhouse muskmelons or cucumbers. In 
this case the staining of the Bordeaux would not 
injure the marketable product since the Bordeaux 
film may be readily washed or wiped off. However, 
Bordeaux mixture could not be termed standard 
for spraying roses in bloom. At that time the Bor- 
deaux stain may injure the market value of the 
bloom more than would the disease that we wish 
to control. In this case, therefore, ammoniacal cop- 
per carbonate or some other colorless fungicide may 
be termed standard. 

Bordeaux Mixtures. The strength used for ten- 
der plants is three pounds of copper sulphate — ^also 
known as blue stone, six pounds of lime, and fifty 
gallons of water. The easiest way to prepare it is 
to dissolve the blue stone thoroughly in twenty-five 
gallons of water. The best quality of unslaked 
lime should be used and slaked in a little water, care 
being taken, however, not to flood it while slaking, 
nor to let it become too dry. When the slaking is 
completed, enough water is added to make twenty- 
five gallons. The lime water and the blue stone so- 
lution are then mixed, pouring in first one part of 
limxe water, then another part of the blue stone; the 
mixture is then strained and used at once. 

For crops with less delicate foliage, the standard 
Bordeaux mixture is 4-4-50; that is, four pounds 



Methods of Control 403 



copper sulphate, four pounds unslaked lime, and fifty 
gallons of water. With greenhouse crops it is not 
always necessary to prepare stock solutions. Only 
enough for immediate use is prepared at one time. 

In preparing Bordeaux the following points 
should be kept in mind : 

( 1 ) Copper sulphate solutions must be kept only 
in vessels of wood, fiber, brass, bronze, or copper. 
They must not be kept in iron or tin vessels, as they 
corrode them. 

(2) It is necessary to use fresh lime, as air- 
slaked lime is useless. 

(3) Bordeaux mixture can be used only when 
freshly mixed. If allowed to stand twelve hours 
after making, it loses all fungicidal value. 

(4) Bordeaux mixture or lime should never be 
strained through burlap. The lint of the burlap 
is likely to work up into the nozzles and clog them. 

(5) Undiluted solutions of copper sulphate or 
lime should never be mixed together. 

(6) Bordeaux mixture should not be prepared 
with hot water. 

Ammoniacal Copper Carbonate, The objection to 
the use of Bordeaux is that it stains the leaves and 
foliage. 

To avoid staining, colorless ammoniacal copper 
carbonate may take the place of Bordeaux. It is 
prepared as follows: 

Copper carbonate 5 ounces 

Ammonia (26° Baum€) 3 pints 

^^^^^ 50 gallons 



404 Diseases of Greenhouse Crops 



The best results are obtained when the copper 
carbonate is first made into a paste with a little 
water. It is then dissolved by adding the ammonia, 
which is diluted with four quarts of water. If 
three pints of ammonia fail to dissolve all the cop- 
per carbonate, more may be used. Ammoniacal cop- 
per carbonate is only effective when used fresh. It 
loses its fungicidal value by standing, as the am- 
monia evaporates quickly. 

Sulphur, Flowers of sulphur are often used to 
control powdery mildew or asparagus rust. It may 
be applied either by hand or with a duster. There 
are a number of other fungicides on the market which 
are not mentioned here. They should be thoroughly 
tested before they are used. 

Combination Sprays. For purposes of economy, 
it is advisable to control both insect pests and fun- 
gous diseases at the same time. Spraying, if prop- 
erly done, is effective in controlling or in keeping 
in check all the pests which attack greenhouse crops. 
In combining a fungicide with an insecticide, we 
may accomplish two aims in one operation. The 
various spray mixtures which may or may not be 
combined are indicated by Cooley and Swingle * — 



Tobacco 
Extracts 



Bordeaux 
Mixture 



Paris green 

Arsenate of lead 

Arsenite of zinc (ortho) 
Arsenite of lime 



yes 
yes 
yes 
yes 



yes 
yes 
no 
yes 



* Cooley, B. A., and Swingle, D. B., Montana Agr. Expt. Sta. 
Circ. 17: 119-151, 1912. 



Methods of Control 405 



Each of these preparations is mixed and applied 
just as if it were used alone. A combination of the 
ammoniacal copper carbonate with an arsenate 
would be unsafe, since the ammonia renders the 
arsenic more soluble, and hence may result in the 
burning of the foliage. However, it may be safely 
mixed with the tobacco products. 

Recent investigations by Professor Safro, En- 
tomologist to the Kentucky Tobacco Products Co., 
indicates that "Black Leaf 40" may be used with- 
out soap in combination with such spray chemicals 
as lime-sulphur, arsenate of lead, arsenite of zinc, 
and iron sulphate, for controlling sucking and chew- 
ing insects and fungous diseases. Professor Safro's 
work further claims that "Black Leaf 40" may be 
safely combined with Bordeaux, and the desired re- 
sults obtained. He writes as follows : "For purposes 
of spraying, add to every one hundred gallons of 
Bordeaux three-fourths of a pint of 'Black Leaf 40.' 
As far as safety to the foliage is concerned, much 
greater strength of nicotine may be added to the 
Bordeaux, but no additional effectiveness will be 
given to the mixture as an insecticide. Any nicotine 
solution which contains four hundredths of one per 
cent nicotine will be effective in controlling plant 
lice if the spraying is thoroughly done." 



PROPORTION OF COMBINED SPRAYS 



Bordeaux and Paris Green 



Paris green 

Bordeaux mixture 



pound 
50 gallons 



J'Arsenite of soda . . 
Bordeaux mixture 



Bordeaux and Arsenite of Soda 



I quart 
50 gallons 



4o6 Diseases of Greenhouse Crops 



Bordeaux mixture must never be combined with 
kerosene emulsion, carbolic acid emulsion, and mis- 
cible oils. 

(d) Fotassium Sulphide, Like sulphur, this is 
a valuable fungicide for the control of the powdery 
mildew. The following strength is recommended: 

Potassium sulphide 4 ounces 

Water 10 gallons 

Potassium sulphide is effective only if used im- 
mediately after it is prepared. It loses its value 
by being exposed for any length of time. 

Stickers. It is well known that with some plants, 
such as cabbage, spray mixtures cannot be made to 
stick. The use of an adhesive added to the spray 
mixture will largely overcome this difficulty. An 
adhesive may be prepared as follows: 

Resin 2 pounds 

Sal soda (crystals) i pound 

Water i gallon 

The resin and the sal soda should be added to 
one gallon of water and boiled in an iron kettle 
for one and a half hours until clear. For plants 
which are hard to wet, such as cabbage or onions, 
the amount of the solution given above should be 
used for each fifty gallons of Bordeaux or ammonia- 
cal copper carbonate. For other plants, this amount 
is added to each one hundred gallons of the spray 
mixture. 



Fig. 8i. Bucket Spray Pump with Long 
Nozzle. 



Methods of Control 407 



Principles Involved in Spraying 

It should be remembered that to destroy chew- 
ing insects, such as caterpillars, etc., the stomach 
poison must be evenly distributed all over the plant. 
This thorough spraying should be done as soon as 
the presence of the pest is suspected. Intelligent 
and observant growers will remember the time of 
appearance of the pest every year, although this date 
depends somewhat on the climate of each season.- 
In destroying the green aphids, the contact poison, 
should be distributed as evenly as possible on the 
insect itself. It is, therefore, best to spray for aphids 
when they are actually found working on the plants. 
To check chewing insects and fungous pests, how- 
ever, the applications are made before the parasites 
appear. Before spraying it is necessary to have 
well in mind which organism is to be destroyed, 
and the proper ingredients to be used. To keep 
fungous pests in check it is necessary to have the 
plant covered with the fungicide all the time infec- 
tion is feared or suspected. This spraying is preven- 
tive, protecting the plant from becoming infected. 
When the parasite has penetrated the host, spraying 
is of little value in saving the infected plant, al- 
though it will protect others which are as yet 
healthy. It is essential that the gardener be always 
ready to spray. Sometimes delay for even a day 
may prevent the attainment of positive results. The 
timely destruction of one insect, or of one spore. 



4o8 Diseases of Greenhouse Crops 



means the elimination of countless generations of 
these pests. 

Thoroughness is as important in spraying as it 
is in everything else in life. Especially is this true 
for the control of fungous diseases. 

Spraying Machines 

Success in spraying often depends on the sprayer, 
and especially on the nozzle. In small scale such as 
under greenhouse conditions, it is next to useless to 
invest in elaborate expensive machinery. A small 
bucket pump with long nozzle (fig. 81) as used by 
Professor Paddock of the Texas Experiment Station 
has given good satisfaction. The Auto Spray No. i 
is a very desirable spraying machine for indoor 
plants. 

Hygienic Considerations 

Since plants are endowed with life they readily 
respond to intelligent hygienic treatment. This is 
especially true with indoor plants, which at best are 
growing under abnormal conditions. Every effort 
should, therefore, be made to create indoors as nearly 
normal conditions as possible. The effect of proper 
sunlight, heat, moisture and ventilation has already 
been discussed under pages 53-85. Cleanliness is also 
an important consideration. The walks, interior 
walls and glass should be kept as clean as possible. 
Old and used pots should be scrubbed and washed 
at least once a year. Dead or infected plants should 



Methods of Control 409 



never find their way on the manure pile. Such 
manure is bound to find its way back and will con- 
taminate the soil in benches and involve later extra 
expenses of soil sterilization. Insects and diseases 
should never be allowed to get a strong foothold. It 
is easy enough to destroy a few aphids for instance, 
but it becomes a matter of greater difficulty to han- 
dle a greenhouse which has become thoroughly in- 
fested. No definite rules can be laid down, but 
every greenhouse man must study his crops and his 
conditions in order to succeed in keeping his plants 
in the best condition of health. 

Selection of Cuttings 

With forced crops, perhaps more than with any 
others under glass, the success of cuttings is largely 
dependent upon proper selection. This is true for 
instance with carnations, roses, violets or chrysan- 
themums. It would scarcely seem possible that the 
nature of the cutting could materially influence the 
future plant. This, however, is a fact which has 
been aptly mentioned by Galloway."^ It must be 
remembered that plants, like animals, are influenced 
by inheritance as well as by environment. In se- 
lecting cuttings the object should be to procure those 
parts of the plant which will transmit with the 
greatest vigor the ability to flower or to fruit as the 
case may be. Experienced growers will appreciate 
this. Frequently in starting with two-rooted cut- 

* Galloway, B. T., Year Book, U. S. Dept. Agr., 247-256, 1895. 



410 Diseases of Greenhouse Crops 



tings from the same plant, grown under the same 
conditions, dissimilar plants are produced. The 
one may be vigorous, blooming freely, while the 
other may be dwarfed and sickly, and produce no 
flowers, or merely a few of an undesirable type. In 
the selection of cuttings, appearance alone should 
not constitute the main guide. A cutting may ap- 
pear vigorous, yet be immature or too old. Violet 
cuttings made from old wood will generally pro- 
duce inferior plants, which will run out within a 
year or be carried off by disease. Violet cuttings 
made from soft, immature wood, will result in weak, 
spindly growth and in plants susceptible to damping 
off. On the other hand, a cutting may be made 
of the proper material, yet if it is too short it will 
also be useless. A violet cutting that is too short 
will not have sufficient anchorage. Each time a 
flower is pulled it will roll around or its roots will 
break (fig. 82, a to c). 

Not only is care necessary in the selection of 
cuttings, but it is also necessary to provide proper 
conditions for growth. A setback at this time may 
result in disappointing returns later. Heat, air, 
light and water should be carefully attended to in 
dealing with soft-wooded cuttings. 



GLOSSARY 



A 

AcERVULUs (Acervuli). A non-sexual, open cup-shaped 

fruiting body of fungi. 
iEciDiosPORES. Spores of rust fungi borne in an iEcidium, 
iEciDiUM (iEcium). A cup-shaped body in which are 

formed the spring spores of certain rust fungi. 
Aerobe. Micro-organisms requiring air, more especially 

oxygen. 

Ammonification. The formation of ammonia at the ex- 
pense of other forms of nitrogen compounds, accom- 
plished through the action of soil micro-organisms upon 
organic substances. 

Ammonifiers. Soil micro-organisms which are capable of 
transforming nitrogen compounds into ammonia. 

Amceboid. Like an amoeba, the creeping movement of 
which is made possible by appendage-like bodies. 

Antheridium. The male sexual organ of fungi. 

Apical. Terminal formation at the point of any fungous 
structure. 

AscospoRE. Spore borne in an ascus. 

Ascus (Asci). Winter sexual spore sac, within which are 

formed the ascospores. 
Arthrospores. Whole vegetative cells of either bacteria 

or fungi which, by a thickening of their wails, become 

resting spores. 

B 

Bacterium (bacteria). Simplest form of plant belonging 
to a low order, lacking chlorophyll, and reproducing by 
means of fission. 



411 



412 Glossary 



Basidiospores. Spores formed on basidia. 
Basidium (basidia). A straight stick-like spore bearing 
fungous thread. 

C 

Canker. Definite dead area in the bark of stems or roots 

of plants. 
Capitate. Possessing a head. 
Carbonaceous. Dark to black colored. 
Chlamydospores. Resting spores of fungi possessing thick 

walls and formed within mycelial cells. 
Chlorophyll. Green coloring matter in leaves of higher 

plants. 

CiLiATE. Fringed with hair. 

CiLiUM (Cilia). Thread-like appendages on bacteria or 
zoospores of myxomycetes, which aid in their movement. 

Columella. Sterile axle of a pillar-like structure within a 
sporangium. 

CoNiDiA (conidium). Spores formed asexually on free 

borne conidiophores. 
CoNiDiOPHORE. A spore bearing fungal stalk. 
Cuticle. The outermost skin of plants. 
Cyst. Incrusted body. 

D 

Deliquescent. Dissolving or melting. 
Diffuse. Loosely spread. 
Dilated. Enlarged. 

E 

Endospore. Spore formed within another cell. 

Entomogenous. Fungi living parasitically on insects. 

Enzyme. An organic chemical product capable of bringing 
about changes, but without itself undergoing any 
change or entering into the final product. 

Exospore. Outer covering of a spore. 



Glossary 413 



F 

Falcate. Sickle shaped. 

Flagella. Whip-like appendage of bacteria or swarm 
spores. 

Fungus (fungi). Plant of very low order with vegetative 
growth (mycelium), reproducing by means of sexual 
and non-sexual spores. 

G 

Glaucus. Sea green. 
GoNiDiA. Algae-like cells. 
GuTTULATE. Drop-like. 

H 

Haustoria (haustoriumj. Special organs of fungi used for 

attachment or for obtaining food. 
Host. Any plant which nourishes a parasite. 
Hyaline. Translucent or colorless. 

HypERTROPHiED. Any part of diseased plant abnormally 
enlarged. 

Hypha (Hyphae). Thread-like vegetative part of fungi. 

I 

Indurated. Hardened. 
Infect. To cause disease. 

Intercellular. Growing between the host cells. 
Intracellular. Growing inside the host cells. 

L 

Lenticel. a special loose corky structure in plants in- 
tended to serve as a medium of exchange of gases. 
Lesion. A definite diseased area. 



414 Glossary 



M 

Macroconidia. Large conidia. 
MiCROCONiDiA. Very small conidia. 

Middle-lamella. The connecting or cementing membrane 

between any two cells of a plant. 
Mycelium. Vegetative threads or hyphse of a fungus. 
Mycology. The study of fungi. 

O 

Omnivorous. Attacking a large variety of plants. 
Oogonium. Female sexual organ of fungi containing one 

or more oospheres. 
OosPHERE. Naked mass of protoplasm developing into 

oospores after fertilization. 
Oospore. Fertilized oosphere. 

P 

Papillate. Possessing wing-like structure. 

Paraphyses. Sterile filaments found in some fruiting 

forms of fungi. 
Parasite. An organism living at the expense of another 

(the host). 
Pathogenic. Producing disease. 
Pedicillate. Borne on a stalk. 

Perithecium. a flask-shaped or globose, sexual fruiting 

body containing asci. 
Peritrichiate. Flagella formed all over the surface of an 

organism. 

PiONNOTES. An effuse conidial stage, containing a max- 
imum of conidia, and a minimum of aerial mycelium. 

Plasmodium. A mass of naked protoplasm with numerous 
nuclei, capable of amoeboid motion. 

Polar flagella. Flagella borne at the pole ends of a 
micro-organism. 



Glossary . 415 



Protoplasm. The living substance of any plant cell. 

PsEUDO. False. 

Pustule. A blister or pimple. 

Pycinidia. Sack-shaped fruiting bodies of a fungus in 
which the pycniospores or summer spores are formed 
non-sexually. 

Pycniospores. Non-sexual summer spores borne in pyc- 
nidia. 

S 

Saprophyte. A micro-organism living on dead organic 
matter. 

ScLEROTiUM (sclerotia). Compact mass of mycelium in a 
dormant state, living over from year to year. 

Septum. Any partition between two cells in the same fun- 
gous filament. 

Set^s:. Bristle-shaped bodies of fungi. 

Soil flora. Bacterial or fungus growth of a soil. 

SoRUS. Heap of spores. 

Sporangiophore. Stalk bearing sporangium. 

Sporangiospores. Spores formed in a sporangium. 

Sporangium. Free, non-sexual bearing spore sack. 

Spore. A cell capable of reproducing a plant like its 
parent. It corresponds in function to the seeds of 
higher plants, 

Stomata. Minute openings in the stems, leaves or fruits 
of plants which serve as a medium of exchange of 
plant gases. 

Stroma. A spore-bearing cushion composed of mycelium 
and sometimes of host tissue. 

Swarm spores. Spores possessed with the power of mo- 
tion, or motility. 

T 

Teleutospores (teliospores), resting or winter spores of 
rust fungi. 

Telium. a sorus in which teleutospores are borne. 



4i6 Glossary 



u 

Uredospores. Summer spores of rust fungi. 

V 

Vesicular. Composed of vessels. 
Viscid. Sticky. 

Z 



ZooGLCE^. Colony imbedded in a gelatinous bed. 
Zoosporangia, Sporangia, which produce zoospores. 
Zoospores. A motile spore. 



INDEX 



Acid soils, treatment, 30 
Actinonema rosae, 325 
Actinomyces chromogenus, 115, 

174 
Adams, 5 

Adianthum cuneatum, 254 

farleyense, 254 

gracillinum, 254 
Aecedium cinerariae, 243 

euphorhiae-g erardianae, 225 

oxalidis, 306 

rubellum, 176 
African marigold, 208 
Agaricus campesiris, 159 
Ali Riza, 265 
Alkali soils, 31 

control, 32 
Alsophila Australis, 254 
Alternanthera, 200 

amena, 65 

cultural considerations, 200 

diseases of, 200 

leaf blight, 200 

root rot, 200 
Alternaria brassicae, 129 

brassicae var. nigrescens, 157 

dianthi, 229 

atiolae, 359 
American Beauty Rose, 75 
Ammonification, 13 
Ammoniacal copper carbonate, 
403 

Anaesthetics, 89 
Anthostomella achira, 216 
Antirrhinum, 201 

anthracnose, 203 

branch blight, 204 

blight, 205 

cultural considerations, 201 
diseases of, 202 
root knot, 205 
rust, 202 



Antirrhinum, wilt, 205 
Ants, 376 

Aphelenchus olesistus, 25 
Aphids, 371 

Aphis gossypii, 137, 372 
Apium graveolens, 129 
Arachnides, 365 
Arsenite of zinc, 382 
Arthur, J. C, 222, 223, 237 
Ascochyta aspidistrae, 206 

chrysanthemi, 241 

fibricola, 243 

hortorum, 143 

lycopersici, 189 

pi si, 169 

primulae, 317 

rhei, 176 

<uiolae, 357 
Asparagus, 108 

cultural considerations, 108 

damping off, 108 

diseases of, 108 

officinalis, 108 

rust, 109 
Aspidiatus nerii, 371 
Aspidistra, 205 

anthracnose, 206 

cultural considerations, 205 

diseases of, 206 

leaf spot, 206 

lurida, 205 
Aspidium falcatum, 258 
Asplenium nidus-avis, 26 
Aster, 207 

cultural considerations, 207 

diseases of, 207 

damping off, 211 

leaf blight, 208 

root knot, 211 

white grub injury, 210 

wilt or stem rot, 209 
Atkinson, G. F., 17, 231, 257 



417 



4i8 



Index 



Available nitrogen and absorp- 
tion of, iz 
Azalea, 211 

cultural considerations, Zii 

diseases of, 212 

indica, 211 

leaf spot, 212 



Bacillus aroideae, 280, 281 
aster ace arum, 208 
caratovorus, 126, 281 
cauHvorus, 263 
coli- communis, 13 
cypripedii, 295, 296^ 
fluorescens liquefaciens, 13 
fluorescens putidus, 13 
hyacinthi septicus, 267 
janthinus, 13 
lathyri, 338 
megatherium, 13 
messentericus fvulgatus, 13 
mycoides, 13 
proteus (vulgaris, 13 
subtilis, 13 

tracheiphillus, 102, 137, 155 
Bacteria, 8 

Bacterium dianthi, 223 

oncidii, 296 
Beach, S. A., 161 
Bean, 30, 110 

anthracnose, 112 

blight, no 

cultural considerations, 110 

diseases of, no 

powdery mildew, n2 

root knot, 114 

root rot, 114 

Sclerotinia rot, iii 
Bees, 100 
Beet, 30, 114 

crown gall, 114 

cultural considerations, 114 

damping off, 116 

diseases of, 114 

downy mildew, 117 

drop, 117 

leaf spot, 117 

root rot, 116, 119 

scab, 115 



Begonia, 26, 213 

cultural considerations, 213 

diseases of, 213 

powdery mildew, 213 

root knot, 214 

root rot, 214 
Berlese, A. N., 352 
Bessey, E. A., 25 
Beta 'vulgaris, 114 
Bidgood, J., 294 
"Black Leaf," 383 
"Black Leaf 40," 383 
Blake, M. A., 73, 75 
Bletia, anthracnose, 301 

leaf spot, 304 
Blodgett, F. H., 226 
Blossom drop, 99 
Bolley, H. L,, 223 
Bordeaux mixture, 402 
Botrytis cinerea, 150 

paeoniae, 285 

^vulgaris, 315 
Brassica oleracea var. botrytis, 
120 

Bremia lactucae, 149 
Brown, Nelly A., 148 
Burkholder, W. H., 114 
Byars, L. P., 271 

Caladium, 214 

cultural considerations, 214 

diseases of, 214 
Calanthe, culture of, 290 
Calceolaria, 215 

arachnoidea, 215 

cultural considerations, 215 

diseases of, 215 
Calendula, 208 
Calla lily, 280 

blight, 282 

cultural considerations, 280 

diseases of, 280 

leaf spot, 282 

soft rot, 280 
Cana, 216 

cultural considerations, 2x6 

fungi, 216 

indica, 216 
Capsicum annum, 169 
Carbon, transformation of, i2 



Index 



419 



Carnation, 217 
Alternaria leaf spot, 229 
anthracnose, 230 
branch rot, 232 
brown stem rot, 232 
bud rot, 228 
cohesion of petals, 222 
cultural considerations, 217 
damping off, 231 
die back, 232 
fertilizer, 4 
leaf mold, 229 
malnutrition, 220 
powdery mildew, 227 
root knot, 234 
root rot, 233 
rust, 224 

rust parasite on, 226 
Septoria leaf spot, 226 
sleep, 219 

splitting of blossoms, 221 

stigmonose, 223 

white tip, 219 

yellows, 221 
Carrots, 30, 120 

cultural considerations, 120 

diseases of, 120 

root rot, 120 

soft rot, 120 
Carum pertroselinum, 166 
Cauliflower, 30, 67, 120 

bacterial leaf rot, 123 

black mold, 129 

black rot, 124 

club root, 122 

cultural considerations, I20 

damping off, 127 

diseases of, 122 

downy mildew, 127 

drop, 128 

ring rot, 128 

root knot, 129 

soft rot, 126 
Celery, 30, 129 

cultural considerations, 129 

diseases of, 130 

early blight, 131 

late blight, 130 

soft rot, 130 
Cellulose, 12 



Ceratophorum setosum, 260 
Cercospora angreci, 304 
apii, 131 

beticola, 117, 118 

caladii, 214 

capsisi, 171 

cheirantht, 362 

lactuae, 153 

resedae, 287 

richardiaecola, 282 

rosicola, 330 

violae, 311, 361 
Chaetomium spirochaete, 344 
Charles, V. K., 249 
Cheiranthus cheiri, 362 
Chittenden, J. T., 205 
Chlorosis, 98 

control of, 99 
Chrysanthemum, 235 

black speck, 236 

blight, 242 

blossom rot, 239 

cultural considerations, 235 

crown gall, 236 

diseases of, 236 

ligule rot, 239 

Phyllosticta leaf spot, 240 

powdery mildew, 243 

ray blight, 241 

rust, 237 

Septoria leaf spot, 241 
Cineraria cruenta, 243 
Cladochytrium <violae, 352 
Cladosporium fulvum, 192 

macro car pum, 179 
Clematis, 244 

anthracnose, 244 

cultural considerations of, 

244 

diseases of, 244 

leaf spot, 244 
Clinton, G. P., 26, 219, 256, 321 
Codiaeum variegatum, 246 
Coelogyne, culture of, 291 
Coleman, 46 

Coleosporium sonchi, 243 
Coleus, 62, 65, 245 

broom rape, 245 

cultural considerations, 245 

damping off, 245 



420 



Index 



Coleus, diseases of, 245 
Colletotrichum antirrhini, 202 

bletiae, 301, 304 

cordylines, 247 

cyclameneae, 249 

dicheae, 303 

kentiae, 308 

lagenarium, 141 

lindemuihianum, ill, 141 

nigrum, 170 

omnivorum, 206, 284 

orchidearum, 303 

phomoides, 191 

primulae, 316 

roseolum, 303 

schizanthi, 332, 333 

violae-tricoloris, 311 
Color of glass, effect on plant 
growth, 59 

effect on temperature, 58 

influencing root development, 

Combination sprays, 404 
Conn, Joel H., 9 
Completoria complens, 257, 258 
Codiaeum variegatum, 246 
Cordyline, 247 
Australis, 247 

cultural considerations, 247 
terminales, 251 
Corticium 'vagum var. solani, 
195 

Craig, J., 237 
Crepin, H., 239 
Crocker, W., 219 
Croton, 246 

anthracnose, 247 

cultural considerations, 246 

diseases of, 246 
Cucumber, 30, 133 

angular leaf spot, 238 

anthracnose, 141 

bacterial wilt, 137 

cultural considerations, 133 

damping off, 138 

diseases of, 133 

downy mildew, 138 

lack of color in fruit, 136 

leaf curl, 134 

malnutrition, 134 



CucuHiber, mosaic, 137 

physiological wilt, 136 

powdery mildew, 140 

root knot, 142 

timber rot, 140 
Cucumis, melo, 154 

saiimis, 133 
Cutworms, 375 

control, 48 
Cyclamen, 248 

anthracnose, 249 

cultural considerations, 248 

diseases of, 248 

leaf spot, 249, 250 

persicum, 248 

root rot, 248 
Cylindrocladium scoparium, 329 
Cylindrosporium chrysanthemi, 
242 

clematidis, 244 

var. Jackmani, 244 
Cypripedia, culture of, 291 
Cypripedium godefroyae, 295 

haynaldium, 295 

laevigatum, 295 

philippinense, 295, 296 
Cysticus racemosus canariensis, 
260 

Cystopus hliti, 119 

Candida, 286 
Cystospora ericeti, 254 

Daffodils, 252 

cultural considerations of, 252 

diseases of, 252 

yellow stripe, 253 
Damping off, 16, 19 

control, 46, 47, 66 

cuttings, 19 

symptoms, 17 
Damon, S. C., 29 
Darlington, H. R., 253 
Darluca filum, 226, 306 
Darner, H. B., 5, 221 
Daucus carota, 120 
Davis, G. C, 372 
Dendrobium, culture of, 292 
Dendrophoma con-vallartae, 285 
Diabrotica mttata, 155, 137 
Dianthus caryophyllus, 217 



Index 



421 



Dictyuchui monosporus, 269 
Diplocarpon rosae, 319, 324, 325 
Diplodia hulbicola, 306 
Diphdia sohraliae, 305 
Diseases, carriers of, loi 
Diseases, physiological, 96 
Doran, W. L., 37 
Dorsett, P. H., 360 
Dracena, 250 

cultural considerations, 250 

diseases of, 250 

fragans, 250 

leaf blotch, 252 

leaf spot, 251, 252 

Phyllosticta leaf spot, 251 

tip blight, 251 
Dry bulb thermometer, 78 

Egg plant, 30, 142 

anthracnose, 143 

damping off, 142 

diseases of, 142 

fruit rot, 142 

root knot, 144 

Southern wilt, 142 
Electric light, effect of, 67 
Electro-culture, 66 
Emulsions, 399 
Enlows, E. M., 137 
Entyloma ellissii, 179 
Erica, 253 

cultural considerations, 253 
Erodium texanum, 263 
Erysiphe dehor ace arum, 140 

polygotii, 112, 156 
Euphorbia pulcherima, 240, 

Exeipularia epidendri, 306 
Exosporium palmworum, 308 

Ferns, 254 

algae, parasites on, 259 
Completoria, damping off, 257 
cultural considerations, 254 
damping off, 256 
diseases of, 255 
leaf scorch, 255 
Phyllosticta leaf spot, 258 
tip burn, 255 
yellows, 256 



Fertilizers, 4 

effect on soil, 6 
Ficus elastica, 331 
Flammarion, Camille, 58, 64 
Fletcher, S. W., 100 
Fumago pagans, 260, 194 
Fumigation "don'ts," 397 
Fungi, 8 
Fungicides, 401 

Funkia undulata var. variegata, 

284 

Fusarium bulbigenum, 288 
incarnatum, 210 
lathyri, 22, 344 
lycopersici, loi, 193, 194 
oxysporum, 194 
'violae, 312, 361 

Galloway, B. T., 263 
Gardenia, 259 

cultural considerations, 259 

jasminoides, 259 
Garman, P., 367 
Genista, 260 

cultural considerations, 260 

diseases of, 260 
Geranium, 260 

broom rape, 265 

cultural considerations, 260 

damping off, 264 

diseases of, 261 

dropsy, 261 

gray mold, 264 

leaf spot, 262, 264 

soft rot, 263 

yellows, 267 
Germination troubles, 104 
Giddings, N. J., 358 
Gleosporium affine, 302 

clemafidis, 244 

crotonis, 247 

epidendri, 303 

laeliae, 303 

macropus, 299 

maxillariae, 303 

melengoneae, 143 

oncidii, 303 

pallidum, 303 

piperatum, 170 

rosae, 326 



422 



Index 



Gleosporium, soraurianum, 247 

stanhopeae, 303 
'violae, 256 
Glomerella cincta, 300 
piperata, 170 

rufomaculans var. Cycla- 
minis, 249, 338, 343 
Gossard, H. A., 377 
Graphiola phoenicisy 307 
Graphium bulbicola, 306 
Grape hyacinth, 272 

cultural considerations, 272 
Grossenbacher, J. G., 156 
Green, S. N., 49 

W. J, 49 
Greenhouse pests, 364 

soil, summer treatment, 48 
Gregg, O. T., 100 
Griffon, M. M., 252, 297 
Gussow, H. T., 275 

Hall, J. G., 230, 320 
Halsted, B. D., 200, 215, 229, 

245, 259, 265, 270, 279, 284, 

300, 304, 308, 326 
Harshberger, J. W., 246 
Harter, L. L., 97 
Hartwell, 29 
Haskins, H. D., 134, 335 
Heald, F. D., 93, 228 
Heat requirements, 71 
Heliothrips haemorrhoidalis, 369 
Hellebore, 382 
Hemileia oncidii, 296 
Hemileia vastatrix, 260 
Henning, P., 297, 298, 305 
Herbert, A., 294 
Heterodera radicicola, 23, 26, 

129, 211, 234, 347 
Heterosporium echinulatum, 229 

variabtle, 179 
Hicks, G. H., 107 
Hodgkiss, H. E., 228 
Hopkins, E. F., 350 
Hori, S., 295 

Hot water sterilization, 37 
Howard, W. L., 86 
Howitt, J. E., 182 
Humaria thozettt, 306 
Humbert, J. G., 35 



Humidity, affected by walks in 
the house, 76 

effect on greenhouse crops, 75 

effect on roses, 73 

relation to greenhouse cul- 
ture, 74 ^ 

the determination of, 77 
Hyacinth, 26 

bulb rot, 270 

damping off, 269 

diseases of, 266 

gumosis, 266 
Hyacinth nematode, 271 

soft white rot, 267 

Sclerotinia rot, 270 
Hyacinthus orientalis, 266 
Hydrangea, 272 

cultural considerations, 27* 

diseases of, 273 

hortensis, 272 

leaf spot, 274 

rust, 273 
Hydrocyanic-acid gas, 385 
Hygienic considerations, 408 
Hypocrella gardeniae, 260 

Insecticides, 381 

Insect infested soil, control, 48 
Inverted pan method, 34 
Iron, changes of, 14 
Isopods, 377 
Istvanffi, G. De, 150 

Japan lily, diseases of, 283 
Jensen, C. M., 332 
Johnson, J., 46 
Jones, L. R., 358 

Kelsey, J. A., 245 
Kentia belmoreana, 308 

canterburyana, 308 

fosteriana, 308 
Kerosene emulsion, 399 
Kirchner, O., 260 
Klobahn, H., 276 
Knap solution, 86 
Knight, L., 219 

Lactuca sativa, 145 
Laelia, culture of, 292 
Lamkey, M. R., 221 



Index 



423 



Lathrop, E. C, 46 

Lathyrus odoratus, 334 
Leaf blight nematode, 25 
Lecanium oleae, 371 

tessellatum, 371 
Leptosphaeria 'vagabunda, 243 
Leptostromella elasticae, 331 
Lettuce, 30, 67, 145 

bacterial blight, 147 

Cercospora leaf spot, 153 

cultural considerations, 145 

diseases of, 146 

downy mildew, 149 

drop, 150 

fertilizer, 5 

gray mold, 150 

Kansas disease, 148 

leaf spot, 152 

root knot, 153 

rosette, 153 

shot hole, 152 

South Carolina disease, 147 
top burn, 147 

Lewis, I. M., 262 

Light, effect on anatomy of 
plants, 63 
effect on construction and 
management of hot-houses, 56 
effect on disease resistance, 66 
effect on lettuce, tomatoes, cu- 
cumbers, roses, carnations, 

effect on transpiration, 63 
pathological relationship, 53, 
55 

rays, effect on color of plants, 
64, 

relation to greenhouse cul- 
ture, 53 ^ 
Light intensities, effect on lettuce, 
69 

effect on plants, 68 

effect on radish, 70 
Lights, colored, effect of, 58 
Lilac, 65, 275 

cultural considerations, 275 

diseases of, 275 

leaf blight, 275 

powdery mildew, 276 

twig blight, 276 



Lilium longiflorum, 277 

speciosum var. rubrum, u,n 
Lily, 277 

Bermuda disease, 278 

Botrytis disease, 279 

cultural considerations, 277 

diseases of, 277 

rust, 279 
Lily of the Valley, 284 

cultural considerations, 284 

diseases of, 284 

leaf spot, 285 

rot, 285 

Septoria leaf spot, 285 
Lime, 30 
Linseed oil, 399 
Lycaste, culture of, 292 
Lycopersicum esculentum, 180 

Maclllaria rufescentis, 298 
Macrophoma cattleyicola, 305 

cor dy lines, 247 

oncidii, 305 

suramensis, 314 
Macrosporium bulbotrichum, 
216^ 

solani, 193 
Magnesium lime, 31 
Malnutrition, 97 

causes of, 97 

control, 98 
Mangin, M. L., 299 
Marguerite, 208 
Marsonia perforans, 152 

'violae, 358 
Massee, G., 238, 283, 288, 293, 

340, 350 
Massey, L. N,, 325 
Maublanc, 252, 297 
McCue, C. A., 383 
Mealy bugs, 370 
Melanconium pandani, 313 
Melchers, I. E., 40, 187 

method of sterilizing soils, 
40 

Mercer, W. B., 227 
Methods of control, 381 
Micro-organisms, number in 
soil, 10 

Microsphaera alni, 276^ 341 



424 



Index 



Mignonette, 286 

cultural considerations, 286 

diseases of, 286 

leaf spot, 287 

root rot, 287 

white rust, 286 
Mikio Kasai, 323 
Milliped, 377 
Mint, 153 

cultural considerations, 153 

diseases of, 153 

rust, 154 
Mites, 366 

Monilia prunosa, 214 
Mosaic, 102 

cause, 102 

control, 103 

symptoms, 102 
Moznette, G. F., 368 
Muncie, F. W., 6 
Muscari botryoides, 272 
Mushroom, 159 

bacterial spot, 161 

cultural considerations, 159 

diseases of, 161 

mycogone disease, 163 
Muskmelon, 30, 154 

anthracnose, 157 

bacterial wilt, 155 

cultural considerations, 154 

downy mildew, 156 

diseases of, 155 

leaf blight, 157 

powdery mildew, 156 

root knot, 158 

Southern blight, 158 
Mycelium, 18 
Mycogone perniciosa, 163 
Mycosphaerella brassicaecola, 
128 

citrullina, 156 
pinodes, 342 
rosignea, 327 

Narcissus, 287 
bulbocodium, 287 
bulb rot, 288 

culiunl considerations, 287 
diseases of, 288 
rust, 288 



Nectophora chrysanthemi co- 

leus, 372 

rosae, 372 
Nectria bulbicola, 298 
Nectria behnickiana, 305 

{Dialonectria) binotiana, 299 

(Dialonectria) bolbophyli, 305 

goroshankianna, 299 

(D.) phyllogena, 299 

pandani, 313 
Nepanthes bicolarata, 306 
Nephrolepsis exaltata, 254 
Nicofume, 366 
Nitrification, 13 
Nitrobacter, 14 
Nitrosococus, 14 
Nitrosomonas, 14 

Odontoglossum, culture of, 292 
Oidium chrysanthemi, 243 
Olpidiiim bras sic ae, 127 
Oncidii dasystelis, 297 
Oncidium, culture of, 292 
Ophiolbolus linosporaides, 216 
Orchids, 290 

American anthracnose, 300 

anthracnose, 299 

bacterial leaf spot, 295 

deterioration, 294 

European anthracnose, 302 

leaf spot, 304 

petal blight, 298 

rot, 298 

rust, 296, 297 

spot disease, 293 
Orobanche minor, 265 

ramosa, 245 
Oscillatoria, 259 
Overhead irrigation, 85 
Oxalis, 306 

boiviei, 306 

cultural considerations, 306 
Oxidus gracilis f 377 

PaliTi anthracnose, 308 

cultural considerations, 306 
diseases of, 307 
Exosporium leaf spot, 308 
leaf blight, 309 
leaf spot, 310 



Index 



425 



Palm smut, 307 
Pammel, L. H,, 21 
Pandanus, cultural considera- 
tions, 313 

diseases of, 313 

<veitchn, 313 
Pansy, 310 

anthracnose, 311 

crown rot, 313 

cultural considerations, 310 

diseases of, 310 

leaf spot, 311 

root rot, 312 
Paris green, 382 
Parsley, 30, 166 

cultural considerations, 166 

diseases of, 166 

drop, 166 

leaf blight, 166 
Patterson, F. W., 249 
Pavarino, G. L., 208 
Pea, 166 

cultural considerations, 166 

diseases of, 167 

garden, 30 

pod spot, 168 

powdery mildew, 168 

Sclerotinia rot, 167 

Thielavia root rot, 167 
Pediculopsis graminum, 22% 
Peglion, v., 296 
Pelargonium, 26 
Peltier, G. L., 20, 222, 233 
Pepper, 30, 169 

anthracnose, 170 

black anthracnose, 170 

cultural considerations, 169 

diseases of, 169 

fruit spot, 170 

leaf spotj^ 171 

Southern blight, 171 

sunburn, 169 
Perforated pipe method, 36 
Pernospora effusa, 178 

Jaapiana, 176 

parasitica, 127, 362 

schachtii, 117 

spars a, 320 

irifoliorum, 339, 340 

<viciae, 340 



Pernospora violae, 353 
Pestalozzia palmarum, 309 

richardiae, 282 
Phalaenopsis amabilis, 295 

culture of, 293 

schilleriana, 295 
Phaseolus 'vulgaris, 109 
Phoenix canariensis, 309 

reclinata, 309 

tenius, 309 
Phoma betae, 120 

cyclamenae, 249, 250 

destructiva, 189 

nepenthis, 306 

poolensis, 203 

solani, 19, 143 

<vexans, 142, 143 
Phosphates, changes of, 14 
Phragmidium americanum, 323 

fusiforme, 323 

japonicum, 323 

rosae muliiflorae, 323 

rosae rugosae, 323 

speciosum, 323 

subcorticum, 322 

yezoense, 323 
Phyllachora vermsegiua, 247 
Phyllosticta amaranthi, 200 

chenopodii, 179 

chrysanthemi, 240 

cordylines, 247 

dracaenae, 251, 252 

hydrangeae, 274 

maculicola, 251 

nepentheacearum, 306 

primulicola, 316, 317 

pteridis, 258, 259 

richardiae, 282 

<violae, ZS7 
Physalospora cattleyae, 299 

herbarum, 305 

orchidearum, 305 
Phytophthora infestans, 186, 
187 

phaseoli, 188 
syringae, 276 
ter re stria, i88, 189 
Pilobolus crystallinus, 236, 237, 
321 

Pisum sativum, 166 



426 



Index 



Plantain lily variegated, blight 
of, 284 

Plant diseases, nature of, 93 
Plant lice, 371 

Plasmodiophora hrassicae, 122 
Pleospora orchidearum, 305 
Poinsettia, 313 
collar rot, 314 

cultural considerations, 313 

diseases of, 314 
Potassium, changes of, 14 

sulphide, 406 
Primrose, 315 

anthracnose, 316 

blight, 316 

cultural consideration!^ 315 

diseases of, 315 

leaf blotch, 317 

leaf spot, 317 

spot decay, 315 
Primula obconia, 316 

sieboldii, 316 

sinensis, 315, 316 
Pseudococcus citri, 370 

longispinus, 370 
Pseudomonas campestris, 124, 
125 

erodii, 262, 263 
fiuorescens, 162 
hyacinthi, 267, 268 
lachrymans, 138 
maculicolunit^ 123, 134 
marginale, 148 
phaseoli, no, in 
solanacearum, 185, 186 
syringae, 275 
teutlium, 119 

tumefaciens, 114, 115, 236, 

320 

viridili'vidum, 147 

<vitans, 147, 148 
Pseudoperonospora cubensis, 138 
Pteris argyria, 258 

cretica, 258 

cretica var. magnifica, 258 
serrulata avistata, 26, 216, 254 
tremula, 26 
wimeseth, 26 
Puccinia antirrhini, 202 
chrysanthemi, 237 



Puccinia eriophori, 243 

menthae, 154 

oxalidis, 306 

phragmitis, 176 

prostii, 349 

schroeteri, 2%Z 

tulipae, 349 

violas, 353 
Pucciniastrum hydrangeae, 273 
Pyrenochaeta bergevini, 206 
Pythium de Baryanum, 17, i8, 

127, 256, 257, 264 
Pythium intermedium, 256, 257 

Radish, 30, 67, 173 

cultural considerations, 173 

damping off, 17^ 17^ 

diseases of, 173 

downy mildew, 175 

root knot, 175 

scab, 174 
Ramularia primulae, 317 
Rand, F. V., 137 
Rane, F. W., 67, 84 
Raphnus sativus, 173 
Razi, Ali, 238 
Reddick, D., 356 
Red spider, 365 
Reseda odorata, 286 
Rest period, breaking of, 86 
Rheo sporangium aphaniderma^ 

turn, 174 
Rhizoctonia root rot, 20 

solani, 19, 20, 21, 119, 153, 
200, 2n, 233, 245, 314, 315, 
.346 

Rhizoglypkus echinops, 279 
Rhizopus necans, 283 
Rhopalosiphum violae, 372 
Rhubarb, 30, 175 

anthracnose, 176 

cultural considerations, 175 

diseases of, 176 

leaf spot, 176 

powdery mildew, 176 

rust, 176 
Roasting or pan firing, 39 
Rogers, S. S., 131 
Root knot, 23t 119 



Index 



427 



Rosa chinensis, 318 
Rose, 318 

anthracnose, 326 

black spot, 324 

blossom blight, 320 

bronzing of leaves, 319 

Cercospora leaf spot, 330 

crown canker, 329 

crown gall, 320 

cultural considerations, 318 

diseases of, 318 

downy mildew, 320 

effect of humidity, 73 

fertilizer, 6 

leaf spot, 327 

mechanical spotting, 321 

powdery mildew, 323 

rust, 322 

Septoria leaf spot, 328 

stem canker, 328 
Rosellinia massinkii, 270 
Rubber plant, 331 

cultural considerations, 331 

diseases of, 331 

leaf spot, 331 
Russell, H. M., 370 

Sackett, W. G., 13 
Sarcina lutea, 13 
Scale insects, 371 
Schreiner, O., 46 
Schizanthus, 332 

anthracnose, 332 

cultural considerations, 332 

diseases of, 332 

pinnatus, 332 
Sclerotinia bulborum, 270 

fuckeliana, 29, 150, 269, 315, 
.239. 

libertiana, 19, iii, 128, 117, 
140, 340, 354 
Sclorotium bulborum, 350 

orchidearum, 306 

rolfsii, 19, 158, 171 

iulipae, 350, 351 

tuliparum, 350, 351 
Screw pine, 313 
Seaver, F. L., 350 
Seed, age of, 104 

cultural considerations, 104 



Seed, diseased, 104 

effect of fertilizer, 106 

storage conditions, 106 

testing, io6 

treatment, 107 

weight and color, 105 
Selby, A. D., 35, 273 
Selections of cuttings, 409 
Shading, effect of, 68 
Shantz, H., 68 
Septoria azaleae, 212 

chrysanthemella, 241 

chrysanthemi, 241 

consimiles, 152 

cyclaminis, 250 

dianthi, 226 

lactucae, 152 

lycopersici, 190, 191 

majalis, 285 

petroselini var. Apii, 130 

rosae, 328 
Shamel, A. D., 34 
Sheldon, J. L., 251 
Sherbakoff, C. D., 188 
Sick soils, 16 

acid, 28 

treatment, 28 
Sling psychroraeter, 77 
Slugs, 378 

Smith, E. F., 267, 310 
Smith, R. E., 207, 312 
Smoke injury, 95 

control, 96 
Soap, 384 

Sobralia raacramtha, 300 
Soil flora, 7 

action on mineral substances, 
14 

and soil fertility, 9 

nature and function, 10 

parasitic, 22 
Soil infesting insects, 375 

treatment, formaldehyde, 33 
Soil sterilization, 32 

changes due to, 45 

effect on plants, 44 

effect on seed germination, 43 

steam, 34 
Solanum melongena, 142 
Solid beds, 84 



428 



Index 



Sorauer, P., 244, 248, 302 

Sorrel, 30 
Sow bugs, 377 
Spaulding, P., 240 
Sphaerella caladii, 214 

gardeniae, 260 

pinodes, 168 
Spherodithis neo <washingtoniae, 
310 

Spinach, 30, 67, 177 

anthracnose, 179 

cultural considerations, 177 

diseases of, 177 

downy mildew, 178 

malnutrition, 177 
Sporonema, 254 

obturatum, 254 
Sporoirichum. anthrophilum, 

22§ 

poae, 228 
Spraying, 381 
Spraying machines, 408 

principles involved, 407 
Steam rake m.ethod, 36 
Stemphylium ericoctonum, 254 
Stevens, F. L., 241, 320 
Stibella bulbicola, 305 
Stickers, 406 
Stomach poisons, 382 
Stone, G. E., 53, 97, 105, 134, 
312 

Stone, R. E., 183, 169 

Stoneman, B., 310 

Stout, A. B., 348 

Striped cucumber beetle, 102 

Stewart, F. C, 204, 213, 225, 

228, 328 
Stewart, V. B., 332 
Stuart, W., 5 
Sturgis, W. C, 232 
Subirrigation, 83 

effect on crops, 84 
Suffocation, 83 
Sulphur, 384, 404 

changes of, 14 
Sunburn, 94 
Sweet pea, 334 

anthracnose, 343 

bud rot, 338 

Chaetomium root rot, 344 



Sweet pea, collar rot, 340 
cultural considerations, 334 
diseases of, 334 
downy mildew, 339 
Fusarium wilt, 344 
malnutrition, 335 
mosaic, 338 

physiological troubles, 334 

powdery mildew, 341 

root knot, 347 

root rot, 346 

spot disease, 342 

stem rot, 340 

streak, 338 

Thielavia root rot, 341 

wilt, 22 
Swingle, D. B., 404 
Syringa vulgaris, 275 

Taft, L. R., 84 
Tarsonemus pallidus, 366 
Taubenhaus, J. J., 103, 305, 334 
Temperature, relation to green- 
house, 74 
Tetranychus, bimaculatus, 365 
Thielama basicola, 167, 341, 

345 
Thrips, 369 
Tile method, 37 
Tobacco, 383 

decoction, 383 
Tolaas, A. S., 162 
Tomato, 180 

anthracnose, 191 

black mold, 194 

black rot, 193 

blossom end rot, 183 

broom rape, 195 

buck eye rot, 188 

cultural considerations, 180 

damping off, 186 

fruit rot, 189 

hollow stem, 181 

injured by fumigation, 199 

late blight, 186 

leaf mold, 192 

leaf spot, 189, 190 

mosaic, 185 

Rhizoctonia fruit rot, 195 
root knot, 195 



Index 



429 



Tomato, sleeping sickness, loi, 
193 

Southern wilt, 185 

sunburn, 184 

winter blight, 182 
Trelease, W., 309 
Trichoderna koningi, 13 
Trkhosporium fuliginosum, 254 
Tubercularia cattleyicola, 306 
Truffant, G., 394 
Tulip, 348 

blindness, 348 

bulb rot, 349 

cultural considerations, 348 

diseases of, 348 

rust, 349 
Sclerotium rot, 350 

smut, 349 
Tulip a suave olens gesneriana, 
348 

Tylenchus dipsaci, 271 



Uredo behnickiana, 297 

cannae, 216 

onicidii, 297 
Urocystis oxalidis, 306 

violae, 353 
Uromyces hetae, 119 

caladii, 214 

caryophyllinus, 224, 232 

scillarum, 272 
Urophlyctis leproides, 119 
Ustilago tulip ae, 349 

vaillantii, Z'jz 

Vanda, culture of, 293 
Veihmeyer, F. J., 163 
Ventilation, 85 



V ermicularia polygoni-mrgin- 
ica, 176 

concentria, 252 
Vinal, S. C, 399, 366 
Viola odoraia, 351 

tricolor, 310 
Violet, 351 

anthracnose, 356 

Cercospora leaf spot, 361 

crown rot, 354 

cultural considerations, 351 

diseases of, 352 

downy mildew, 353 

leaf spot, 357 

mold, 353 

root rot, 352, 354, 361 
rust, 353 

speck anthracnose, 358 
spot disease, 359 
white mold, 258 
Volutella dianthi, 231 

Waksman, L. A., lo, 13 
Wallflower, 362 

cultural considerations, 362 
Ward, M., 17 
Warren, G. F,, 199 
Water requirements, 7« 
Wheeler, H. J., 5 
White fly, 371 
White fly fumigation, 199 
White grubs, 375 
Wireworms, 375 
Wooden beds, prevention of 

rot, 84 
Wood lice, 377 
Woods, A. F., 223, 279 
Wolf, F. A., 325, 362 

Zygodesmus albidus, 358 
Zythia nepenthis, 306 



^'^a,me„t Date cJcr^Jf"" OxL 



